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Abstract:

For the purpose of providing a urethane(meth)acrylate excellent in
emulsifiability in water and a production method thereof, and a light
curable aqueous emulsion using the urethane(meth)acrylate having a low
viscosity and excellent in the curability, provided is a
urethane(meth)acrylate being represented by the following general formula
(1) and having a weight average molecular weight of 1,000 to 10,000:
A1-O--(CONH--B1-NHCOO--C1-O)n-CONH--B1-NH--COO-D1 (1)
wherein in formula (1), n represents a natural number of 1 to 30, A1
represents a residue of a hydroxyl group-containing (meth)acrylate, B1
represents a residue of diisocyanate, C1 represents a residue of a diol
of an acyclic hydrocarbon or a cyclic hydrocarbon, and D1 represents a
residue of a polyoxyalkylene glycol monoalkyl ether.

Claims:

1. A urethane(meth)acrylate being represented by the following general
formula (1) and having a weight average molecular weight of 1,000 to
10,000: A1-O--(CONH--B1--NHCOO--C1--O)n--CONH--B.sup-
.1--NH--COO-D1 (1) wherein in formula (1), n represents a natural
number of 1 to 30, A1 represents a residue of a hydroxyl
group-containing (meth)acrylate, B1 represents a residue of
diisocyanate, C1 represents a residue of a diol of an acyclic
hydrocarbon or a cyclic hydrocarbon, and D1 represents a residue of
a polyoxyalkylene glycol monoalkyl ether.

2. The urethane(meth)acrylate according to claim 1, obtained by allowing
to react with each other the hydroxyl group-containing (meth)acrylate,
the diisocyanate, the diol of the acyclic hydrocarbon or the cyclic
hydrocarbon and the polyoxyalkylene glycol monoalkyl ether.

3. The urethane(meth)acrylate according to claim 1, wherein the
diisocyanate is one or more selected from the group consisting of
isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated
xylylene diisocyanate and hydrogenated diphenylmethane diisocyanate.

4. The urethane(meth)acrylate according to claim 1, wherein the number of
carbon atoms in the diol of the acyclic hydrocarbon or the cyclic
hydrocarbon is 6 to 20.

5. The urethane(meth)acrylate according to claim 4, wherein the diol,
having a number of carbon atoms of 6 to 20, of the acyclic hydrocarbon or
the cyclic hydrocarbon is one or more selected from the group consisting
of 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol,
1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol,
1,15-pentadecanediol, 1,18-octadecanediol, 1,19-nonadecanedioi,
1,20-eicosanediol, polypropylene glycol, aliphatic polycarbonate polyol,
aliphatic polyester polyol, aliphatic polycaprolactone diol, hydrogenated
bisphenol A, ethylene oxide-modified hydrogenated bisphenol A, propylene
oxide-modified hydrogenated bisphenol A, 1,4-cyclohexanediol and
tricyclodecanedimethanol.

6. The urethane(meth)acrylate according to claim 1, wherein the hydroxyl
group-containing (meth)acrylate is at least one of polypropylene glycol
mono(meth)acrylate, pentaerythritol tri(meth)acrylate and
dipentaerythritol penta(meth)acrylate.

7. The urethane(meth)acrylate according to claim 1, wherein the
polyoxyalkylene glycol monoalkyl ether is represented by the following
general formula (2): HO--(CH2CH2O)m--R (2) wherein in
formula (2), R represents an alkyl group and m represents a natural
number of 9 to 90.

8. A cross-linked urethane(meth)acrylate comprising a constitutional unit
including the urethane(meth)acrylate according to claim 1.

9. The cross-linked urethane(meth)acrylate according to claim 8, prepared
by cross-linking with a bifunctional or higher functional cross-linking
agent.

10. The cross-linked urethane(meth)acrylate according to claim 9, wherein
the cross-linking agent is a mercapto group-containing compound.

11. A light curable aqueous emulsion comprising: a urethane(meth)acrylate
according to claim 1 or a cross-linked urethane(meth)acrylate according
to claim 8; and the compound having a radical polymerizable group(s) and
the photoradical polymerization initiator emulsified and dispersed with
the urethane(meth)acrylate or the cross-linked urethane(meth)acrylate.

12. The light curable aqueous emulsion according to claim 11, wherein the
compound having a radical polymerizable group(s) is a compound having in
the molecule thereof three or more (meth)acryloyl groups.

13. The light curable aqueous emulsion according to claim 11, wherein the
photoradical polymerization initiator is a hydrophobic
photopolymerization initiator.

14. The light curable aqueous emulsion according to claim 11, wherein the
photoradical polymerization initiator comprises two or more photoradical
polymerization initiators including at least a thioxanthone-based
photoradical polymerization initiator.

15. The light curable aqueous emulsion according to claim 11, wherein the
compound having a radical polymerizable group(s) comprises a
urethane(meth)acrylate for fixing.

16. The light curable aqueous emulsion according to claim 11, further
comprising a fluorescent brightening agent.

17. A production method of the urethane(meth)acrylate according to claim
1, the method comprising: a first step of obtaining a first reaction
product represented by the following general formula (1a),
OCN--(B1--NHCOO--C1--O)n--CONH--B1--NCO (1a) by
allowing the diisocyanate and the dial of the acyclic hydrocarbon or the
cyclic hydrocarbon to react with each other; a second step of obtaining a
second reaction product represented by the following general formula
(1b), OCN--(B1--NHCOO--C1--O)n--CONH--B1--NH--COO-D.-
sup.1 (1b) by allowing the first reaction product and the polyoxyalkylene
glycol monoalkyl ether to react with each other; and a third step of
allowing the second reaction product and the hydroxyl group-containing
(meth)acrylate to react with each other.

18. The production method of the urethane(meth)acrylate according to
claim 17, wherein; in the first step, the molar ratio between the
diisocyanate and the dial of the acyclic hydrocarbon or the cyclic
hydrocarbon is 5:1 to 5:4; in the second step, the molar ratio between
the first reaction product and the polyoxyalkylene glycol monoalkyl ether
is 1:0.5 to 1:1; and in the third step, the molar ratio between the
second reaction product and the hydroxyl group-containing (meth)acrylate
is 1:1.5 to 1:1.

19. A production method of the cross-linked urethane(meth)acrylate
according to claim 8, further comprising a fourth step of allowing the
urethane(meth)acrylate represented by the foregoing general formula (1),
obtained by the production method according to claim 17, and the
bifunctional or higher functional cross-linking agent to react with each
other.

20. The production method of the cross-linked urethane(meth)acrylate
according to claim 19, wherein in the fourth step, a compound having in
the molecule thereof three or more (meth)acryloyl groups is further
allowed to react with the bifunctional or higher functional cross-linking
agent.

21. The production method of the cross-linked urethane(meth)acrylate
according to claim 19, wherein in the fourth step, a
urethane(meth)acrylate for fixing is further added.

22. The production method of the cross-linked urethane(meth)acrylate
according to claim 20, wherein in the fourth step, the ratio between the
content of the urethane(meth)acrylate represented by the foregoing
general formula (1) and the compound having in the molecule thereof three
or more (meth)acryloyl groups and the content of the bifunctional or
higher functional cross-linking agent is 100:1 to 100:10 in terms of
mass.

[0003] The present invention relates to a urethane(meth)acrylate and a
production method thereof, a cross-linked urethane(meth)acrylate and a
production method thereof, and a light curable aqueous emulsion.

[0004] 2. Description of the Related Art

[0005] Nowadays, due to the VOC (Volatile Organic Compounds) regulation
and for the purpose of coping with this regulation, approaches to
development of aqueous paints, adhesives, coating materials and the like
free of organic solvents have been more actively performed than ever. In
heat curable and ultraviolet curable paints, adhesives, coating materials
and the like, oil-based multifunctional urethane(meth)acrylates having
two or more (meth)acryloyl groups have hitherto been frequently used;
however, recently, hydrophilic urethane(meth)acrylates have been
attracting attention as materials for aqueous paints, adhesives, coating
materials and the like.

[0006] Examples of such disclosed hydrophilic urethane(meth)acrylates
include: a multifunctional urethane(meth)acrylate having, in the main
chain, polyethylene oxide groups as hydrophilic groups and having two or
more (meth)acryloyl groups at both terminals of the main chain; and a
multifunctional urethane(meth)acrylate having a structure in which the
main skeleton is a polyisocyanate having three or more isocyanate groups,
and a molecular chain having at least one hydrophilic group and a
molecular chain having at least two or more (meth)acryloyl groups are
branched.

[0007] Among such urethane(meth)acrylates, as an example of the
urethane(meth)acrylate having (meth)acryloyl groups at both terminals of
the main chain, there is a hydrophilic urethane acrylate, disclosed in
Japanese Patent Laid-Open No. 02-199102, using as the starting materials
polyester polyol, isophorone diisocyanate and 2-hydroxydipropyl acrylate.
As an example of a urethane(meth)acrylate having a branched structure,
there is a hydrophilic urethane acrylate, disclosed in Japanese Patent
Laid-Open No. 2007-191529, using as the starting materials a trimer of
hexamethylene diisocyanate, pentaerythritol triacrylate and polyethylene
glycol monomethyl ether.

[0008] However, it has never been possible to say that existing
hydrophilic urethane(meth)acrylates are sufficient with respect to
emulsifiability in water and emulsion stability in water. When the
aqueous emulsion of such a urethane(meth)acrylate is used in aqueous
paints, adhesives, coating materials and the like, the resulting
materials tend to be high in viscosity, tend to undergo the occurrence of
the variation of the viscosity depending on the production lot, and
further, have sometimes been poor in long term stability with respect to
the particle size distribution, the coating film performances and the
like.

[0009] Aqueous emulsions of the aforementioned existing
urethane(meth)acrylates are generally cured by dissolving a water-soluble
photopolymerization initiator and by ultraviolet light irradiation after
drying water. In this case, when water remains, the ultraviolet light
irradiation sometimes result in no curing or insufficient curing.
Commercially available water-soluble photopolymerization initiators are
limited with respect to the amount dissolved in water, and hence the
improvement of the curability is limited. On the other hand, hydrophobic
photopolymerization initiators have also been used as dispersed in the
water media of the aqueous emulsions of existing urethane(meth)acrylates;
however, there occur the problems such as that the photopolymerization
initiators are limited with respect to the amount dispersed in water
media, or that the photopolymerization initiators are precipitated with
time.

SUMMARY OF THE INVENTION

[0010] Accordingly, the present invention takes as its object the
provision of a urethane(meth)acrylate excellent in emulsifiability in
water and a production method thereof, a cross-linked
urethane(meth)acrylate and a production method thereof, and a light
curable aqueous emulsion using the urethane(meth)acrylate and the
cross-linked urethane(meth)acrylate having a low viscosity and excellent
in the curability, for the purpose of solving these problems.

[0011] The present inventors made a diligent study for the purpose of
solving the aforementioned problems. Consequently, the present inventors
have perfected the present invention by discovering that the
aforementioned problems can be solved by a urethane(meth)acrylate having
a linear structure in which the structure derived from diisocyanate and
the structure derived from diol are arranged on a straight line, wherein
the urethane(meth)acrylate has a molecular structure in which a
hydrophobic moiety and a hydrophilic moiety are located respectively at
the opposite terminals of the linear main chain of the
urethane(meth)acrylate.

[0012] Specifically, the present invention is as follows.

[0013] [1] A urethane(meth)acrylate being represented by the following
general formula (1) and having a weight average molecular weight of 1,000
to 10,000:

A1-O--(CONH--B1--NHCOO--C1--O)n--CONH--B1--NH---
COO-D1 (1)

wherein in formula (1), n represents a natural number of 1 to 30, A1
represents a residue of a hydroxyl group-containing (meth)acrylate,
B1 represents a residue of diisocyanate, C1 represents a
residue of a diol of an acyclic hydrocarbon or a cyclic hydrocarbon, and
D1 represents a residue of a polyoxyalkylene glycol monoalkyl ether.

[0014] [2] The urethane(meth)acrylate according to [1], obtained by
allowing to react with each other the hydroxyl group-containing
(meth)acrylate, the diisocyanate, the diol of the acyclic hydrocarbon or
the cyclic hydrocarbon and the polyoxyalkylene glycol monoalkyl ether.

[0015] [3] The urethane(meth)acrylate according to [1], wherein the
diisocyanate is one or more selected from the group consisting of
isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated
xylylene diisocyanate and hydrogenated diphenylmethane diisocyanate.

[0016] [4] The urethane(meth)acrylate according to [1], wherein the number
of carbon atoms in the diol of the acyclic hydrocarbon or the cyclic
hydrocarbon is 6 to 20.

[0017] [5] The urethane(meth)acrylate according to [4], wherein the diol,
having a number of carbon atoms of 6 to 20, of the acyclic hydrocarbon or
the cyclic hydrocarbon is one or more selected from the group consisting
of 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol,
1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol,
1,15-pentadecanediol, 1,18-octadecanediol, 1,19-nonadecanediol,
1,20-eicosanediol, polypropylene glycol, aliphatic polycarbonate polyol,
aliphatic polyester polyol, aliphatic polycaprolactone diol, hydrogenated
bisphenol A, ethylene oxide-modified hydrogenated bisphenol A, propylene
oxide-modified hydrogenated bisphenol A, 1,4-cyclohexanediol and
tricyclodecanedimethanol.

[0018] [6] The urethane(meth)acrylate according to [1], wherein the
hydroxyl group-containing (meth)acrylate is at least one of polypropylene
glycol mono(meth)acrylate, pentaerythritol tri(meth)acrylate and
dipentaerythritol penta(meth)acrylate.

[0019] [7] The urethane(meth)acrylate according to [1], wherein the
polyoxyalkylene glycol monoalkyl ether is represented by the following
general formula (2):

HO--(CH2CH2O)m--R (2)

wherein in formula (2), R represents an alkyl group and m represents a
natural number of 9 to 90.

[0020] [8] A cross-linked urethane(meth)acrylate comprising a
constitutional unit including the urethane(meth)acrylate according to
[1].

[0021] [9] The cross-linked urethane(meth)acrylate according to [8],
prepared by cross-linking with a bifunctional or higher functional
cross-linking agent.

[0022] [10] The cross-linked urethane(meth)acrylate according to [9],
wherein the cross-linking agent is a mercapto group-containing compound.

[0023] [11] A light curable aqueous emulsion including: a
urethane(meth)acrylate according to [1] or a cross-linked
urethane(meth)acrylate according to [8]; and the compound having a
radical polymerizable group(s) and the photoradical polymerization
initiator emulsified and dispersed with the urethane(meth)acrylate or the
cross-linked urethane(meth)acrylate.

[0024] [12] The light curable aqueous emulsion according to [11], wherein
the compound having a radical polymerizable group(s) is a compound having
in the molecule thereof three or more (meth)acryloyl groups.

[0025] [13] The light curable aqueous emulsion according to [11], wherein
the photoradical polymerization initiator is a hydrophobic
photopolymerization initiator.

[0026] [14] The light curable aqueous emulsion according to [11], wherein
the photoradical polymerization initiator includes two or more
photoradical polymerization initiators including at least a
thioxanthone-based photoradical polymerization initiator.

[0027] [15] The light curable aqueous emulsion according to [11], wherein
the compound having a radical polymerizable group(s) includes a
urethane(meth)acrylate for fixing.

[0028] [16] The light curable aqueous emulsion according to [11], further
including a fluorescent brightening agent.

[0029] [17] A production method of the urethane(meth)acrylate according to
[1], the method comprising:

[0030] a first step of obtaining a first reaction product represented by
the following general formula (1a),

OCN--(B1--NHCOO--C1--O)n--CONH--B1--NCO (1a)

by allowing the diisocyanate and the diol of the acyclic hydrocarbon or
the cyclic hydrocarbon to react with each other;

[0031] a second step of obtaining a second reaction product represented by
the following general formula (1b),

OCN--(B1--NHCOO--C1--O)n--CONH--B1--NH--COO-D1
(1b)

by allowing the first reaction product and the polyoxyalkylene glycol
monoalkyl ether to react with each other; and

[0032] a third step of allowing the second reaction product and the
hydroxyl group-containing (meth)acrylate to react with each other.

[0033] [18] The production method of the urethane(meth)acrylate according
to [17], wherein:

[0034] in the first step, the molar ratio between the diisocyanate and the
diol of the acyclic hydrocarbon or the cyclic hydrocarbon is 5:1 to 5:4;

[0035] in the second step, the molar ratio between the first reaction
product and the polyoxyalkylene glycol monoalkyl ether is 1:0.5 to 1:1;
and

[0036] in the third step, the molar ratio between the second reaction
product and the hydroxyl group-containing (meth)acrylate is 1:1.5 to 1:1.

[0037] [19] A production method of the cross-linked urethane(meth)acrylate
according to [8], further comprising a fourth step of allowing the
urethane(meth)acrylate represented by the foregoing general formula (1),
obtained by the production method according to [17], and the bifunctional
or higher functional cross-linking agent to react with each other.

[0038] [20] The production method of the cross-linked
urethane(meth)acrylate according to [19], wherein in the fourth step, a
compound having in the molecule thereof three or more (meth)acryloyl
groups is further allowed to react with the bifunctional or higher
functional cross-linking agent.

[0039] [21] The production method of the cross-linked
urethane(meth)acrylate according to [19], wherein in the fourth step, a
urethane(meth)acrylate for fixing is further added.

[0040] [22] The production method of the cross-linked
urethane(meth)acrylate according to [20], wherein in the fourth step, the
ratio between the content of the urethane(meth)acrylate represented by
the foregoing general formula (1) and the compound having in the molecule
thereof three or more (meth)acryloyl groups and the content of the
bifunctional or higher functional cross-linking agent is 100:1 to 100:10
in terms of mass.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The invention will be described with reference to the accompanying
drawings, wherein like numbers reference like elements.

[0042] FIG. 1 is a schematic diagram macroscopically illustrating the
light curable aqueous emulsion of the present invention; and

[0044] Hereinafter, the embodiments for implementing the present invention
are described in detail. The present invention is not limited to the
following embodiments and can be implemented in various modifications
within the scope of the gist of the present invention.

[0045] In the present specification, the "emulsifiability" means a
property such that phase separation occurs or precipitation occurs when a
light curable aqueous emulsion is allowed to stand still at 40°
C.; the "curability" means a property such that polymerization and curing
occur in the presence or absence of a photopolymerization initiator as a
result of light irradiation; the "hydrolyzability" means a property such
that hydrolysis occurs; and the "hydrophobic photopolymerization
initiator" means a photopolymerization initiator having a solubility in
water of 0.1% by mass or less.

[0046] Also, in the present specification, "(meth)acrylate" means at least
either of an acrylate and a methacrylate corresponding to the acrylate,
and "(meth)acryloyl" means at least either of an acryloyl and a
methacryloyl corresponding to the acryloyl.

[0047] Urethane(Meth)Acrylate

[0048] An embodiment of the present invention relates to a
urethane(meth)acrylate.

[0049] Constitution

[0050] The urethane(meth)acrylate of the present embodiment has a weight
average molecular weight of 1,000 to 10,000 and is represented by the
following general formula (1):

A1-O--(CONH--B1--NHCOO--C1--O)n--CONH--B1--NH---
COO-D1 (1)

wherein in formula (1), n represents a natural number of 1 to 30, A1
represents a residue of a hydroxyl group-containing (meth)acrylate,
B1 represents a residue of diisocyanate, C1 represents a
residue of a diol of an acyclic hydrocarbon or a cyclic hydrocarbon, and
D1 represents a residue of a polyoxyalkylene glycol monoalkyl ether.

[0051] The residue as referred to herein means, in the structure of the
starting material of the urethane(meth)acrylate represented by the
foregoing general formula (1), the moiety not including the functional
group forming the urethane bond; specifically, the residue means the
moiety (represented by A1) not including the hydroxyl group in the
case of the hydroxyl group-containing (meth)acrylate, the moiety
(B1) not including the isocyanate group in the case of diisocyanate,
the moiety (C1) not including the hydroxyl group in the case of the
diol of an acyclic hydrocarbon or a cyclic hydrocarbon, and the moiety
(D1) not including the hydroxyl group in the case of the
polyoxyalkylene glycol monoalkyl ether.

[0052] The weight average molecular weight of the urethane(meth)acrylate
represented by the foregoing general formula (1) can be derived by
measuring the molecular weight distribution on the basis of gel
permeation chromatography (GPC). The weight average molecular weight as
referred to in the present specification means the weight average
molecular weight determined relative to polystyrene standards, and is
measured with a GPC (HLC-8220 (trade name), manufactured by Tosoh
Corporation) in which serially-connected three columns TSK-gel Super
HZM-M (exclusion limit molecular weight: 4×106, molecular
weight fraction range: 266 to 4×106, number of theoretical
stages: 16,000 stages/column, packing material: styrene-based copolymer,
packing particle size: 3 μm) are used.

[0053] The weight average molecular weight of the urethane(meth)acrylate
represented by the foregoing general formula (1) is 1,000 to 10,000 and
preferably 2,000 to 8,000. When the weight average molecular weight falls
within the aforementioned range, the urethane(meth)acrylate tends to form
micelles, is excellent in self-emulsifiability, and further there is
obtained an advantageous effect such that hydrophobic substances tend to
be included within the micelles. This is probably because the adoption of
the urethane(meth)acrylate represented by the foregoing general formula
(1) provides a satisfactory balance between hydrophilicity and
hydrophobicity.

[0054] In the foregoing general formula (1), n represents a natural number
of 1 to 30. The specific numerical value of n is determined by regulating
the aforementioned weight average molecular weight.

[0055] Hydroxyl Group-Containing (Meth)Acrylate

[0056] The hydroxyl group-containing (meth)acrylate is a compound which
gives the structure of A1 in the foregoing general formula (1). The
hydroxyl group-containing (meth)acrylate is used for the purpose of
introducing a polymerizable group(s) into the foregoing general formula
(1). Specifically, the hydroxyl group-containing (meth)acrylate used in
the present embodiment is a compound having one or more (meth)acryloyl
groups and one hydroxyl group, and the urethanation reaction of the
hydroxyl group with one isocyanate group in the diisocyanate introduces a
(meth)acryloyl group(s) to one terminal of the main chain of the
urethane(meth)acrylate of the present embodiment. The introduction of at
least one (meth)acryloyl group enables photopolymerization (photocuring),
and the introduction of two or more (meth)acryloyl groups increases the
photopolymerization rate and provides an advantageous effect to increase
the hardness of the cured product.

[0058] The bifunctional monohydroxydi(meth)acrylate is not particularly
limited; however, examples of the monohydroxydi(meth)acrylate include
glycerol di(meth)acrylate.

[0059] The trifunctional or higher functional
monohydroxypoly(meth)acrylate is not particularly limited; however,
examples of the monohydroxypoly(meth)acrylate include pentaerythritol
tri(meth)acrylate and dipentaerythritol penta(meth)acrylate.

[0060] Because an emulsion having a low viscosity is obtained, preferable
among these is polypropylene glycol mono(meth)acrylate and more
preferable among these is polypropylene glycol monoacrylate. On the other
hand, particularly because an emulsion excellent in curability is
obtained, preferable as the hydroxyl group-containing (meth)acrylate is
at least either of pentaerythritol tri(meth)acrylate and
dipentaerythritol penta(meth)acrylate.

[0061] The aforementioned hydroxyl group-containing (meth)acrylates may be
used each alone or in combinations of two or more thereof.

[0062] Diisocyanate

[0063] The diisocyanate is a compound which gives the structure of B1
in the foregoing general formula (1). The diisocyanate means an organic
diisocyanate having two reactive isocyanate groups in one molecule
thereof.

[0064] A urethane(meth)acrylates synthesized by using an organic
polyisocyanate having three or more isocyanate groups in the molecule
thereof tends to be high in molecular weight and tends to be high in
viscosity. The emulsion (aqueous emulsion) prepared by emulsifying in
water such a urethane(meth)acrylate having the following structure also
tends to be high in viscosity of emulsion (aqueous emulsion): the
concerned structure has a hydrophilic group in the molecule of the
urethane(meth)acrylate, wherein the main chain is formed of a
polyisocyanate having three or more isocyanate groups, and the branched
chains are formed of a molecular chain having at least one hydrophilic
group and a molecular chain having at least two or more (meth)acryloyl
groups.

[0065] On the contrary, the urethane(meth)acrylate synthesized by using a
diisocyanate having two isocyanate groups in the molecule thereof has a
linear structure in which: the structure derived from the diisocyanate
and the structure derived from the diol are linearly arranged; and as
shown in the foregoing general formula (1), there is at one terminal a
hydrophilic group derived from polyoxyalkylene glycol monoalkyl ether,
and there is arranged at the other terminal a hydrophobic moiety in which
to a structure derived from a (meth)acrylate having one or more
(meth)acryloyl group and one hydroxyl group, a structure derived from the
diol of an acyclic hydrocarbon or a cyclic hydrocarbon having two
hydroxyl groups in the molecule thereof is bonded through diisocyanate by
urethane bond. Because of such a structure as described above, the
urethane(meth)acrylate synthesized by using a diisocyanate having two
isocyanate groups in the molecule thereof is particularly excellent in
emulsifiability in water and can drastically reduce the viscosity of the
emulsion (aqueous emulsion) as compared to the emulsions of the
aforementioned conventional urethane(meth)acrylates.

[0066] The diisocyanate is not particularly limited; however, examples of
the diisocyanate include: diisocyanates having an alicyclic hydrocarbon
skeleton such as isophorone diisocyanate; diisocyanates having an
aliphatic hydrocarbon skeleton such as hexamethylene diisocyanate;
diisocyanates having an aromatic hydrocarbon skeleton such as xylylene
diisocyanate, tolylene diisocyanate and diphenylmethane diisocyanate; and
diisocyanates having a hydrogenated aromatic hydrocarbon skeleton such as
hydrogenated xylylene diisocyanate and hydrogenated diphenylmethane
diisocyanate.

[0067] Because there is obtained an advantageous effect such that the
cured product of the urethane(meth)acrylate hardly undergoes yellowing
due to sun light (ultraviolet light), preferable among these
diisocyanates are one or more selected from the group consisting of
isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated
xylylene diisocyanate and hydrogenated diphenylmethane diisocyanate.

[0068] The aforementioned diisocyanates may be used intramolecularly or
intermolecularly each alone or in combinations of two or more thereof.

[0069] Diol of Acyclic Hydrocarbon or Cyclic Hydrocarbon

[0070] The diol of an acyclic hydrocarbon or a cyclic hydrocarbon is a
compound which gives the structure of C1 in the foregoing general
formula (1). The diol is introduced for the purpose of regulating the
degree of the hydrophobicity of the hydrophobic moiety of the
urethane(meth)acrylate represented by the foregoing general formula (1).
The diol is selected so as to provide a satisfactory hydrophobicity. As
specific examples, one or more diols selected from the group consisting
of aliphatic, alicyclic and aromatic diols each having two hydroxyl
groups in one molecule thereof are preferably used; more preferable among
such diols are diols exhibiting satisfactory hydrophobicity.
Specifically, because of being particularly excellent in the concerned
hydrophobicity, the number of the carbon atoms in the diol of the acyclic
hydrocarbon or the cyclic hydrocarbon is preferably 6 to 20.

[0071] It is also possible to select as the diols, according to the
intended use or intended purpose, those diols which are appropriate for
controlling the rigidity or flexibility of the urethane(meth)acrylate and
exhibit satisfactory hydrophobicity.

[0072] As the aforementioned aliphatic diols, heretofore known aliphatic
diols can be used without imposing any particular restrictions as long as
the aliphatic diols do not have in the molecule thereof any aromatic
structure or any alicyclic structure. Specific examples of the aliphatic
diol include: 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol,
1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol,
1,14-tetradecanediol, 1,15-pentadecanediol, 1,18-octadecanediol,
1,19-nonadecanediol, 1,20-eicosanediol, polypropylene glycol (such as
dipropylene glycol and tripropylene glycol), aliphatic polycarbonate
polyol, aliphatic polyester polyol and aliphatic polycaprolactone diol.

[0073] As the aforementioned aromatic diols, heretofore known aromatic
diols can be used without imposing any particular restrictions as long as
the aromatic diols have in the molecule thereof an aromatic structure.
Specific examples of the aromatic diol include: biphenyl-4,4'-diol,
1,4-benzenediol, bisphenol A, ethylene oxide-modified bisphenol A,
propylene oxide-modified bisphenol A, aromatic polycarbonate polyol and
aromatic polyester polyol.

[0074] As the aforementioned alicyclic diols, heretofore known alicyclic
diols can be used without imposing any particular restrictions as long as
the alicyclic diols have in the molecule thereof an alicyclic structure.
Specific examples of the alicyclic diol include: hydrogenated bisphenol
A, ethylene oxide-modified hydrogenated bisphenol A, propylene
oxide-modified hydrogenated bisphenol A, 1,4-cyclohexanediol,
tricyclodecanedimethanol, alicyclic polycarbonate polyol and alicyclic
polyester polyol.

[0075] Because satisfactory emulsification in water is achieved and the
cured product of the urethane(meth)acrylate hardly undergoes yellowing
due to sun light (ultraviolet light), preferable among these are
aliphatic diols and alicyclic diols. Preferable among the aliphatic diols
are one or more selected from the group consisting of 1,8-octanediol,
1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol,
1,13-tridecanediol, 1,14-tetradecanediol, 1,15-pentadecanediol,
1,18-octadecanediol, 1,19-nonadecanediol, 1,20-eicosanediol,
polypropylene glycol, aliphatic polycarbonate polyol, aliphatic polyester
polyol and aliphatic polycaprolactone diol. Preferable among the
alicyclic diols are one or more selected from the group consisting of
hydrogenated bisphenol A, ethylene oxide-modified hydrogenated bisphenol
A, propylene oxide-modified hydrogenated bisphenol A, 1,4-cyclohexanediol
and tricyclodecanedimethanol.

[0076] The aforementioned diols may be used intramolecularly or
intermolecularly each alone or in combinations of two or more thereof.

[0077] Polyoxyalkylene Glycol Monoalkyl Ether

[0078] The polyoxyalkylene glycol monoalkyl ether is a compound which
gives the structure of D1 in the foregoing general formula (1).
Polyoxyalkylene glycol monoalkyl ether is a compound in which one
hydroxyl group of polyoxyalkylene glycol is blocked with an alkyl group,
and is represented by the following general formula (2):

HO--(CH2CH2O)m--R (2)

wherein in formula (2), R represents an alkyl group and m represents a
natural number of 9 to 90.

[0079] The urethanation reaction of the hydroxyl group with one isocyanate
group in the diisocyanate introduces the hydroxyl group to one terminal
of the main chain of the urethane(meth)acrylate of the present
embodiment. Consequently, the urethane(meth)acrylate of the present
embodiment has a structure of an amphiphilic substance which has a
hydrophilic moiety at one terminal of the linear main chain of the
substance, and has a hydrophobic moiety constituted of one or more
polymerizable (meth)acryloyl groups and hydrophobic groups at the other
terminal of the linear main chain; thus, the urethane(meth)acrylate
becomes particularly excellent in emulsifiability in water.

[0080] Because there is obtained an advantageous effect such that the
hydrophilicity can be optionally regulated, the polyoxyalkylene glycol
monoalkyl ether preferably includes in the molecule thereof a
polyoxyethylene structure.

[0081] The polyoxyethylene structure is the repeated structure of the
oxyethylene group. The average repetition number of the oxyethylene
groups, namely, m in the foregoing general formula (2) is determined by
regulating the balance between hydrophilicity and hydrophobicity so as to
result in satisfactory emulsification in water of the
urethane(meth)acrylate of the present embodiment, and is preferably a
natural number of 9 to 90, more preferably a natural number of 9 to 60
and furthermore preferably a natural number of 9 to 30.

[0083] It is also possible to use polyoxyalkylene glycol monoalkyl ethers
including in the molecules thereof, in addition to the polyoxyethylene
structure, other polyoxyalkylene structures. In this case, it is
preferable for emulsification that the polyoxyethylene structure be
located on the side of the terminal alkyl group. Examples of the
polyoxyalkylene structure usable in this case together with the
polyoxyethylene structure include the polyoxypropylene structure and the
polyoxytetramethylene structure. The repetition number of the oxyalkylene
group of the polyoxyalkylene structure used together with the
polyoxyethylene structure is appropriately determined in consideration of
the balance between hydrophilicity and hydrophobicity of the concerned
urethane(meth)acrylate.

[0084] The terminal alkyl group of the polyoxyalkylene glycol monoalkyl
ether, namely, R in the foregoing general formula (2) is preferably a
methyl group, an ethyl group or a propyl group, and more preferably a
methyl group because the smaller is the number of carbon atoms of the
alkyl group, the more the hydrophobicity is lowered and the more
excellent is the emulsifiability.

[0085] The aforementioned polyoxyalkylene glycol monoalkyl ethers may be
used each alone or in combinations of two or more thereof.

[0086] The urethane(meth)acrylates may also be used each alone or in
combinations of two or more thereof, in a below-described light curable
aqueous emulsion.

[0087] The content of the urethane(meth)acrylate is preferably 5 to 50% by
mass and more preferably 10 to 40% by mass in relation to the total
amount (100% by mass) of the light curable aqueous emulsion, for the
purpose of enabling to form coating film and for the purpose of obtaining
coating film performances such as satisfactory film strength and
satisfactory adhesion, when the light curable aqueous emulsion of the
present embodiment is used in aqueous paints, adhesives, coating
materials and the like.

[0088] As described above, according to the present embodiment, a
urethane(meth)acrylate excellent in self-emulsifying capability and
emulsifiability can be provided.

[0089] Cross-Linked Urethane(Meth)Acrylate

[0090] The cross-linked urethane(meth)acrylate according to an embodiment
of the present invention has a constitutional unit including the
urethane(meth)acrylate of the aforementioned embodiment. The cross-linked
urethane(meth)acrylate having as the constitutional unit the
urethane(meth)acrylate represented by the general formula (1) is
excellent in curability and more excellent in the storage stability of
the emulsion.

[0091] Cross-Linking Agent

[0092] The aforementioned cross-linked urethane(meth)acrylate can be
obtained by allowing the urethane(meth)acrylate of the aforementioned
embodiment and a bifunctional or higher functional cross-linking agent to
react with each other.

[0093] The use of a cross-linking agent enables to increase the molecular
weight of the urethane(meth)acrylate. Thus, it is possible to obtain a
cross-linked urethane(meth)acrylate more excellent in curability and more
excellent in the storage stability of the emulsion.

[0094] Gelification can be prevented by performing the reaction, neither
in a solvent system nor in a solvent-free system, but in the oil system
(oil phase) in an O/W emulsion.

[0095] The aforementioned bifunctional or higher functional crosslinking
agent is preferably hydrophobic because this cross-linking agent reacts
with the (meth)acryloyl group. In other words, the aforementioned
bifunctional or higher functional crosslinking agent undergoes the
Michael addition, in the oil phase of an emulsion, to the (meth)acryloyl
group in the urethane(meth)acrylate represented by the general formula
(1), and thus cross-links the concerned urethane(meth)acrylate.

[0096] Examples of such a cross-linking agent reacting with the
(meth)acryloyl group include cross-linking agents having thiol groups or
amino groups in the molecules thereof. Among such cross-linking agents,
either of a multifunctional thiol compound and a multifunctional amine
compound is preferable because of the capability of allowing the reaction
to proceed rapidly, a multifunctional thiol compound being more
preferable.

[0097] The aforementioned bifunctional and higher functional crosslinking
agent is not particularly limited; however, examples of such a
crosslinking agent include mercapto group-containing compounds and amino
group-containing compounds. Preferable among these compounds are mercapto
group-containing compounds because of being low in solubility in water
and tending to be incorporated into the oil phase when dispersed in
water.

[0099] The content of the aforementioned bifunctional or higher functional
cross-linking agent is preferably 3 to 10% by mass and more preferably 5
to 8% by mass in relation to the total mass (100% by mass) of the
(meth)acryloyl group-containing resin.

[0100] The "(meth)acryloyl group-containing resin" as referred to in the
present specification means all the resins that contain the
(meth)acryloyl groups undergoing cross-linking due to the aforementioned
crosslinking agents. Accordingly, the concerned (meth)acryloyl
group-containing resin includes the urethane(meth)acrylate represented by
the foregoing general formula (1) and the below-described compound having
three or more (meth)acryloyl groups in the molecule thereof.

[0101] Production Method of Urethane(Meth)Acrylate

[0102] An embodiment of the present invention relates to a production
method of a urethane(meth)acrylate. The present embodiment can be
rephrased as a production method of the urethane(meth)acylate according
to the aforementioned embodiment.

[0103] The production method of the urethane(meth)acrylate according to
the present embodiment includes a first step, a second step and a third
step.

[0104] In the first step, a first urethane bond-containing reaction
product represented by the following general formula (1a) by allowing the
diisocyanate and the diol of an acyclic hydrocarbon or a cyclic
hydrocarbon preferably having 6 to 20 carbon atoms to react with each
other:

OCN--(B1--NHCOO--C1--O)n--CONH--B1--NCO (1a)

In the first step, the molar ratio between the diisocyanate and the diol
of an acyclic hydrocarbon or a cyclic hydrocarbon having 6 to 20 carbon
atoms is preferably 5:1 to 5:4 and more preferably 5:2 to 5:3.

[0105] In the second step, a second reaction product represented by the
following general formula (1b) is obtained by allowing the first reaction
product and the polyoxyalkylene glycol monoalkyl ether to react with each
other:

OCN--(B1--NHCOO--C1--O)n--CONH--B1--NH--COO-D1
(1b)

In the second step, the molar ratio between the first reaction product
and the polyoxyalkylene glycol monoalkyl ether is preferably 1:0.5 to 1:1
because of resulting in satisfactory emulsification in water.

[0106] In the third step, the second reaction product and the hydroxyl
group-containing (meth)acrylate are allowed to react to each other. In
the third step, the molar ratio between the second reaction product and
the hydroxyl group-containing (meth)acrylate is preferably 1:1.5 to 1:1
and more preferably 1:1.4 to 1:1.2.

[0107] As described above, according to the present embodiment, a
production method of a urethane(meth)acrylate excellent in
self-emulsifying capability and emulsifiability can be provided.

[0108] Production Method of Cross-Linked Urethane(Meth)Acrylate

[0109] The production method of a cross-linked urethane(meth)acrylate
according to one embodiment of the present invention is a production
method of the cross-linked urethane(meth)acrylate of the aforementioned
embodiment. The concerned production method includes a fourth step in
which the urethane(meth)acrylate represented by the general formula (1),
obtained by performing the first step to the third step and the
aforementioned bifunctional or higher functional cross-linking agent are
allowed to react with each other, so that the concerned
urethane(meth)acrylate is cross-linked.

[0110] In the fourth step, in addition to the urethane(meth)acrylate
represented by the foregoing general formula (1), the aforementioned
compound having in the molecule thereof three or more (meth)acryloyl
groups may also be allowed to react with the bifunctional or higher
functional cross-linking agent.

[0111] In the fourth step, a urethane(meth)acrylate for fixing may further
be added. In particular, when the substrate is made of polyvinyl chloride
(hereinafter, also referred to as "PVC"), it is preferable to further add
a urethane(meth)acrylate for fixing. Specifically, when a PVC substrate
is used, the coating film (to be described below) is required to have
adhesiveness to the PVC substrate. In this connection, the addition of
the urethane(meth)acrylate for fixing makes satisfactory the adhesiveness
to the substrate, and hence it can be said that the use of the
urethane(meth)acrylate for fixing is preferable.

[0112] When a substrate made of a material other than PVC, for example,
polyethylene terephthalate (PET) is used, the curability is made more
satisfactory and the storage stability of the emulsion is more excellent
because of the reason that the particles are fined, and hence the content
(addition amount) of the urethane(meth)acrylate for fixing is preferably
low, and the content of the compound having three or more (meth)acryloyl
groups is preferably set at a correspondingly larger value.

[0113] In the fourth step, the ratio between the content of the
urethane(meth)acrylate represented by the foregoing general formula (1)
and (when present) the compound having in the molecule thereof three or
more (meth)acryloyl groups and the content of the bifunctional or higher
functional cross-linking agent is preferably 100:1 to 100:10 and more
preferably 100:5 to 100:8 in terms of mass. When the content ratio is
equal to or more than the lower limit of the aforementioned range, the
curability and the storage stability come to be more excellent. When the
content ratio is equal to or less than the upper limit of the
aforementioned range, the occurrence of undissolved substances can be
prevented, and the vanishing of the (meth)acryloyl group in the system is
prevented and thus the curability can be maintained more satisfactory.

[0114] As described above, in the fourth step, the urethane(meth)acrylate
represented by the foregoing general formula (1), the bifunctional or
higher functional cross-linking agent such as a multifunctional thiol
monomer, and one or more, as the optional components, selected from the
group consisting of the compound having in the molecule thereof three or
more (meth)acryloyl groups, the urethane(meth)acrylate for fixing, the
photoradical polymerization initiator preferably included
thioxanthone-based initiators and the fluorescent brightening agent are
mixed together, and the resulting mixture is emulsified (dispersed in
water) by dropwise adding water to the mixture. The obtained emulsion is
heated, for example, at 80° C. for 6 hours, and consequently the
Michael addition reaction is accelerated to yield the cross-linked
urethane(meth)acrylate.

[0115] In this case, the compound having a (meth)acryloyl group and the
cross-linking agent react with each other and consequently the compound
having a (meth)acryloyl group is cross-linked. In other words, the
cross-linking agent reacts not only with the urethane(meth)acrylate but
with the compound having a (meth)acryloyl group. Accordingly, in the
structure of the cross-linked urethane(meth)acrylate, there can be
concomitantly present various cross-linked compounds such as a compound
resulting from the mutual cross-linking of the urethane(meth)acrylates
represented by the general formula (1), a compound resulting from the
cross-linking between the urethane(meth)acrylate represented by the
general formula (1) and the (meth)acryloyl group-containing compound,
which is an included substance, and a compound resulting from the mutual
crosslinking of the (meth)acryloyl group-containing compounds, which are
included substances. The included substance as referred to herein means a
substance present in the interior of a micelle when an emulsion is formed
and a micelle structure is obtained.

[0116] As described above, when the compound having a (meth)acryloyl group
and the cross-linking agent are allowed to react with each other, there
occur a case where the whole of the compound having a (meth)acryloyl
group is cross-linked and a case where part of the compound having a
(meth)acryloyl group is cross-linked and the rest of the compound having
a (meth)acryloyl group remains uncross-linked. A catalyst may also be
used for the purpose of further accelerating the aforementioned Michael
addition reaction.

[0117] Light Curable Aqueous Emulsion

[0118] An embodiment of the present invention relates to a light curable
aqueous emulsion. The light curable aqueous emulsion includes: at least
either of the urethane(meth)acrylate represented by the general formula
(1) of the aforementioned embodiment and the cross-linked
urethane(meth)acrylate of the aforementioned embodiment; and a compound
having a radical polymerizable group(s) (preferably, a radical
polymerizable (meth)acrylate) and a photoradical polymerization initiator
(photoradical polymerization initiator) emulsified and dispersed in water
by at least either of the concerned urethane(meth)acrylate and the
concerned cross-linked urethane(meth)acrylate. The urethane(meth)acrylate
represented by the general formula (1) of the aforementioned embodiment
and the cross-linked urethane(meth)acrylate of the aforementioned
embodiment are amphiphilic substances, and hence it is made possible to
obtain a light curable aqueous emulsion achieving advantageous effects
such that the emulsion is stable and excellent in dispersibility and is
low in viscosity.

[0119] Hereinafter, "the urethane(meth)acrylate of the aforementioned
embodiment" means both of the urethane(meth)acrylate represented by the
general formula (1) and the aforementioned cross-linked
urethane(meth)acrylate.

[0120] The aforementioned effects due to the light curable aqueous
emulsion of the present embodiment are probably brought about by the
following reasons.

[0121] FIG. 1 is a schematic diagram macroscopically illustrating an
ultraviolet curable aqueous emulsion of an example of the light curable
aqueous emulsion of the present embodiment; and FIG. 2 is a schematic
diagram microscopically illustrating the ultraviolet curable aqueous
emulsion of an example of the light curable aqueous emulsion of the
present embodiment. As shown in FIGS. 1 and 2, the urethane(meth)acrylate
of the aforementioned embodiment probably forms micelles in water in such
a way that the hydrophobic moiety is directed toward the core and the
hydrophilic moiety is directed toward the water phase to form the shell
layer, and thus the urethane(meth)acrylate probably can form in water
micelles including the compound having a radical polymerizable group(s)
(preferably radical polymerizable (meth)acrylate) and the photoradical
polymerization initiator.

[0122] Such a micelle formation as described above is probably ascribable
to the molecular structure of the urethane(meth)acrylate of the
aforementioned embodiment. Specifically, in the micelle formation, the
molecular structure of the urethane(meth)acrylate of the aforementioned
embodiment is smaller in steric hindrance as compared to the case where
the main chain is branched or the main chain has hydrophobic moieties at
both terminals thereof, and is probably free from bend conformation.
Accordingly, it becomes possible that the urethane(meth)acrylate is
regularly densely oriented with the hydrophilic moiety directed toward
the water phase. Thus, in the micelle in which the urethane(meth)acrylate
molecules are densely oriented, the hydrogen bonds between the urethane
bonds operate effectively to increase the micelle formation strength
(packing property) so as to probably contribute to the stability and the
dispersibility of the micelles.

[0123] Probably thus, the light curable aqueous emulsion is excellent in
stability and a satisfactory photopolymerizability is obtained even when
the compound having a radical polymerization group(s) (preferably,
radical polymerizable (meth)acrylate) and the photoradical polymerization
initiator are included in the micelles.

[0124] Compound Having Radical Polymerizable Group(s)

[0125] The compound having a radical polymerizable group(s) used in the
present embodiment undergoes a reaction in a chain-like manner, under the
attack of the below-described initiator radical generated by the
irradiation of light having a specific wavelength (a specific wavelength
range). At the same time, the acryloyl group(s) of the
urethane(meth)acrylate of the aforementioned embodiment present in the
same uniform field as the field in which the radical polymerizable
compound is present also undergoes a reaction in a chain-like manner. In
this way, the light curable aqueous emulsion of the present embodiment
forms a cured coating film on the substrate.

[0126] Examples of the radical polymerizable group(s) in the compound
having a radical polymerizable group(s) include a (meth)acryloyl group, a
vinyl group, a vinyl ether group and a mercapto group.

[0127] As the compound having a radical polymerizable group(s) used in the
present embodiment, a compound having in the structure thereof one or
more (meth)acryloyl groups is particularly preferable, and a compound
having in the structure thereof one or more acryloyl groups is more
preferable. The compound having one or more radical polymerizable groups
includes a monomer having a molecular weight of about a few hundreds,
oligomers ranging from a dimer to a lower polymer consisting of several
monomer units, having a molecular weight of approximately several
thousands or less, and polymers having a molecular weight of several tens
of thousands or less.

[0130] Among these, compounds having in the molecule thereof three or more
(meth)acryloyl groups are more preferable as the compound having a
radical polymerizable group(s) because such compounds are excellent in
photopolymerizability.

[0132] The aforementioned compound having in the molecule thereof three or
more (meth)acryloyl groups is not particularly limited; however, examples
of such a compound include: oligomers having a molecular weight of
approximately several thousands or less and having three or more
(meth)acryloyl groups such as polyester(meth)acrylate,
polyurethane(meth)acrylate (with the proviso that the aforementioned
urethane(meth)acrylate is excluded), epoxy(meth)acrylate, polyether
(meth)acrylate, oligo(meth)acrylate, alkyd (meth)acrylate and polyol
(meth)acrylate; oligomers having in the molecule thereof three or more
acryloyl groups and having a molecular weight of approximately several
thousands or less; and polymer and dendrimer type (meth)acrylates having
a molecular weight of approximately several ten thousands or less.

[0133] The aforementioned compounds having a radical polymerizable
group(s) may be used each alone or in combinations of two or more
thereof.

[0134] Because the compound having a radical polymerizable group(s)
imparts high photopolymerizability (curability) to the light curable
aqueous emulsion, the compound having a radical polymerizable group(s) is
included preferably in a content of 1 to 60% by mass and more preferably
5 to 50% by mass in relation to the total amount (100% by mass) of the
light curable aqueous emulsion.

[0135] Urethane(Meth)Acrylate for Fixing

[0136] The aforementioned compound having a radical polymerizable group(s)
preferably includes a urethane(meth)acrylate for fixing. Thus, when a
coating film including an emulsion is formed on a PVC substrate, the
fixability (adhesiveness) of the coating film is made more excellent. As
described above, because the compound having a radical polymerizable
group(s) preferably includes a compound excellent in
photopolymerizability (curability), it is preferable to use a
urethane(meth)acrylate for fixing, making the adhesiveness more
satisfactory, in combination with the concerned compound.

[0137] It is to be noted that the concerned urethane(meth)acrylate for
fixing is different from the urethane(meth)acrylate represented by the
foregoing general formula (1).

[0138] As described below, the urethane(meth)acrylate for fixing is
constituted of a diisocyanate, a diol component having an aromatic
skeleton and a hydroxyl group-containing (meth)acrylate.

[0139] The weight average molecular weight of the urethane(meth)acrylate
for fixing is particularly preferably 1,000 to 10,000 and more preferably
3,000 to 8,000. When the weight average molecular weight falls within the
aforementioned range, the urethane(meth)acrylate for fixing is excellent
in the adhesiveness of the coating film to the PVC substrate and
satisfactory with respect to the stability of the emulsion.

[0140] Hydroxyl Group-Containing (Meth)Acrylate

[0141] The hydroxyl group-containing (meth)acrylate is used for the
purpose of introducing polymerizable groups. Specifically, the hydroxyl
group-containing (meth)acrylate used in the present embodiment has one or
more (meth)acryloyl groups and one hydroxyl group, and the urethanation
reaction of the hydroxyl group-containing (meth)acrylate with an
isocyanate group introduces one or more (meth)acryloyl groups to each of
the both terminals of the main chain of the urethane(meth)acrylate for
fixing. The introduction of at least one (meth)acryloyl group enables
curing (photopolymerization), and the introduction of two or more
(meth)acryloyl groups enables the increase of the curing rate and enables
the increase of the hardness of the cured product.

[0143] The aforementioned hydroxyl group-containing (meth)acrylate may be
used each alone or in combinations of two or more thereof.

[0144] Diisocyanate

[0145] The diisocyanate is not particularly limited; however, examples of
the diisocyanate include: diisocyanates having a alicyclic hydrocarbon
skeleton such as isophorone diisocyanate; diisocyanates having an
aliphatic hydrocarbon skeleton such as hexamethylene diisocyanate;
diisocyanates having an aromatic hydrocarbon skeleton such as xylylene
diisocyanate, tolylene diisocyanate and diphenylmethane diisocyanate; and
diisocyanates having a hydrogenated aromatic hydrocarbon skeleton such as
hydrogenated xylylene diisocyanate and hydrogenated diphenylmethane
diisocyanate.

[0146] Because the cured product of the urethane(meth)acrylate for fixing
hardly undergoes yellowing due to sun light (ultraviolet light),
preferable among these diisocyanates are one or more selected from the
group consisting of isophorone diisocyanate, hexamethylene diisocyanate,
hydrogenated xylylene diisocyanate and hydrogenated diphenylmethane
diisocyanate.

[0147] The aforementioned diisocyanates may be used intramolecularly or
intermolecularly each alone or in combinations of two or more thereof.

[0148] Diol Component Having Aromatic Skeleton

[0149] As the diol having an aromatic skeleton, heretofore known diols
having an aromatic skeleton can be used without imposing any particular
restrictions as long as the diols have in the molecule thereof an
aromatic structure. Specific examples of the diol having an aromatic
skeleton include: biphenyl-4,4'-diol, 1,4-benzenediol, bisphenol A,
ethylene oxide-modified bisphenol A, propylene oxide-modified bisphenol
A, aromatic polycarbonate polyol and aromatic polyester polyol.

[0150] Preferable among these is aromatic polyester polyol, because of
being more satisfactory in the adhesiveness to the PVC substrate.
Isophthalate is more preferable among aromatic polyester polyols.

[0151] The aforementioned diols may be used intramolecularly or inter
molecularly each alone or in combinations of two or more thereof.

[0152] The content of the urethane(meth)acrylate of the aforementioned
embodiment is preferably 0.5 to 4% by mass and more preferably 1 to 3% by
mass in relation to the total amount (100% by mass) of the light curable
aqueous emulsion because of being more excellent in the adhesiveness to
the PVC substrate and the stability after dispersion in water.

[0153] Photoradical Polymerization Initiator

[0154] The photoradical polymerization initiator used in the present
embodiment causes photoradical polymerization as follows: the
photocleavage, hydrogen abstraction or the like due to the irradiation of
the photoradical polymerization initiator with an active energy ray such
as ultraviolet light (UV) produces a radical (photoradical polymerization
initiator radical), and the radical attacks the urethane(meth)acrylate of
the aforementioned embodiment, the cross-linked urethane(meth)acrylate of
the aforementioned embodiment and the compound having a radical
polymerizable group(s) (preferably a radical polymerizable
(meth)acrylate) to cause photoradical polymerization.

[0155] The photoradical polymerization initiator is preferably a
hydrophobic photopolymerization initiator because the hydrophobic
photopolymerization initiator exhibits a satisfactory emulsifying
dispersibility when emulsified and dispersed in water with the
urethane(meth)acrylate of the present embodiment.

[0158] When the light curable aqueous emulsion of the present embodiment
is used for a material such as a paint, an adhesive or a coating
material, the light curable aqueous emulsion is frequently required to be
cured to the deep portion of the applied material; among the
aforementioned photoradical polymerization initiators, the
phenylphosphine-based photoradical polymerization initiators exhibiting
absorption in a wavelength range from 360 nm to 410 nm are preferably
used for curing of thick films. Specifically, examples of such initiators
preferably include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and
bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Examples of the
commercially available products of such initiators include DAROCUR TPO
(manufactured by BASF Corp.), Speedcure TPO (manufactured by Lambson
Group Ltd.) and IRGACURE 819 (manufactured by BASF Corp.).

[0159] The photoradical polymerization initiators may be used each alone
or in combinations of two or more thereof. The photoradical
polymerization initiator is included in a content of preferably 1 to 10%
by mass, more preferably 3 to 10% by mass and further preferably 5 to 10%
by mass in relation to the total amount (100% by mass) of the light
curable aqueous emulsion. In particular, the range within 5 to 10% by
mass results in satisfactory curability.

[0160] In particular, when two or more photoradical polymerization
initiators are used, such initiators preferably include at least a
thioxanthone-based photoradical polymerization initiator, and more
preferably includes both of a phenylphosphine-based photoradical
polymerization initiator and a thioxanthone-based photoradical
polymerization initiator. In this case, because the thioxanthone-based
photoradical polymerization initiator is excellent in sensitization
effect, the curability is made more excellent.

[0161] The thioxanthone-based photoradical polymerization initiator is not
particularly limited; however, examples of such an initiator include
thioxanthone, 2-methylthioxanthone, 2,4-diethylthioxanthone,
2-isopropylthioxanthone, 4-isopropylthioxanthone, 2-chlorothioxanthone
and 2,4-diethylthioxanthone.

[0162] Examples of the commercially available product of the
thioxanthone-based photoradical polymerization initiator include:
KAYACURE DETX-S (trade name of 2,4-diethylthioxanthone, manufactured by
Nippon Kayaku Co., Ltd.), Speedcure DETX (trade name of
2,4-diethylthioxanthone, manufactured by Lambson Ltd.) and KAYACURE ITX
(trade name of 2-/4-isopropylthioxanthone, manufactured by Nippon Kayaku
Co., Ltd.).

[0163] Fluorescent Brightening Agent

[0164] The light curable aqueous emulsion of the present embodiment
preferably further includes a fluorescent brightening agent in addition
to the photoradical polymerization initiator. Thus, the curability is
made more excellent.

[0165] The fluorescent brightening agent used in the present embodiment is
classified as a sensitizer. The fluorescent brightening agent is a
colorless or slightly colored compound capable of absorbing light having
a peak wavelength approximately in a range from near ultraviolet to short
wavelength visible light, namely, a wavelength range from 300 to 450 nm
and capable of emitting fluorescence having a peak wavelength
approximately in a range from 400 to 500 nm. The fluorescent brightening
agent is also known as the fluorescent whitening agent. The physical
principles and the chemical properties of the fluorescent brightening
agent is described in Ullmann's Encyclopedia of Industrial Chemistry,
Sixth Edition, Electronic Release, Wiley-VCH, 1998.

[0166] The fluorescent brightening agent is excited to an excited state
with an active energy ray and can accelerate the generation of useful
groups such as radicals and acids through the interactions such as energy
transfer and electron transfer with other substances such as radical
generating agents and acid generating agents. Examples of the case of the
occurrence of such interactions include a case where the energy level of
the triplet excited state of the fluorescent brightening agent molecule
and the energy level of the triplet excited state of the radical
generating agent or the acid generating agent are extremely close to each
other, and additionally, the energy level of the triplet excited state of
the radical generating agent or the acid generating agent is slightly
lower than the energy level of the triplet excited state of the
fluorescent brightening agent. Actually, it is required that the
fluorescent brightening agent be capable of capturing the irradiation
light in a wavelength band of from 350 nm to 450 nm, and additionally,
the energy level of the triplet excited state of the fluorescent
brightening agent have the aforementioned specific relation with the
energy level of the triplet excited state of the radical generating agent
or the acid generating agent. In order to meet this requirement, it is
required that the energy level of the singlet exited state and the energy
level of the triplet excited state be close to each other. Accordingly,
also included is the case where the fluorescent brightening agent is used
from the viewpoint of the interaction with the radical generating agent
or the acid generating agent, and at the same time, the absorption
wavelength band of the photoradical polymerization initiator overlaps
with the absorption wavelength band of the fluorescent brightening agent
from the viewpoint of the generation efficiency, as the ink liquid, of
the radical or acid with respect to the irradiation wavelength. In this
case, the fluorescent brightening agent in the present embodiment has an
absorption region in the wavelength band at least partially overlapping
with the absorption wavelength band of the photopolymerization initiator,
capable of performing cleavage thereof.

[0167] The fluorescent brightening agent is not particularly limited;
however, examples of the fluorescent brightening agent include:
naphthalene benzoxazolyl derivatives, thiophene benzoxazolyl derivatives,
stilbene benzoxazolyl derivatives, coumarin derivatives, styrene biphenyl
derivatives, pyrazolone derivatives, stilbene derivatives, styryl
derivatives of benzene and biphenyl, bis(benzazol-2-yl) derivatives,
carbostyrils, naphthalimides, derivatives of
dibenzothiophene-5,5'-dioxide, pyrene derivatives and pyridotriazoles.
These may be used each alone or in combinations of two or more thereof.

[0168] Examples of the commercially available product of the fluorescent
brightening agent used in the present embodiment include TINOPAL OB
manufactured by BASF Corp. and HOSTALUX KCB
(1,4-bis(2-benzoxazolyl)naphthalene) manufactured by Clariant (Japan)
K.K.

[0169] The fluorescent brightening agent used in the present embodiment
has a feature such that the maximum absorbance of the fluorescent
brightening agent per a predetermined concentration in a wavelength band
of from 360 nm to 420 nm is larger than the maximum absorbance per the
same concentration as the aforementioned predetermined concentration of
the photopolymerization initiator in the aforementioned wavelength band.
The present inventors have found that the fulfillment of this feature
results in an ink composition extremely excellent in curability.

[0170] In the design method for allowing the photopolymerization initiator
and the fluorescent brightening agent to fulfill the aforementioned
feature, the absorption spectrum, and the maximum absorbance and the peak
wavelength of the absorption spectrum of each of the photopolymerization
initiator to be used and the fluorescent brightening agent to be used are
analyzed. Then, it is only required to verify whether or not the relation
between the maximum absorbance of the photopolymerization initiator and
the maximum absorbance of the fluorescent brightening agent fulfills the
aforementioned feature.

[0171] When an ultraviolet light-emitting diode (LED) is used as the light
source used for measuring the absorption spectra of the fluorescent
brightening agent and the photopolymerization initiator, LEDs having a
light emission peak in a wavelength band of from 360 nm to 420 nm are
usable. The wavelength of the LED is not limited to the wavelength in the
case where a single LED is used; a plurality of LEDs may be used in
combination so as for the light source to have a plurality of light
emission peaks. For example, LEDs respectively having the peak
wavelengths of 365 nm, 385 nm, 395 nm and 405 nm may be used in
combinations of two or more thereof.

[0172] The fluorescent brightening agents may be used each alone or in
combinations of two or more thereof. The fluorescent brightening agent is
included preferably in a content of 0.01% by mass to 0.5% by mass in
relation to the total mass (100% by mass) of the light curable aqueous
emulsion. When the content falls within this range, the light curability
is made satisfactory, and the effect of the fluorescent brightening agent
itself possibly exerting on the hue of the cured film can be reduced.

Preparation Method of Light Curable Aqueous Emulsion

[0173] As for the light curable aqueous emulsion of the present
embodiment, a person having ordinary skill in the art may select
appropriate methods by appropriately improving and modifying the methods
performed in the below described examples; thus, heretofore known methods
such as emulsion polymerization, high pressure emulsification and phase
inversion emulsification may be adopted. Within the range not impairing
the advantageous effects of the present invention, heretofore known
various emulsifying agents and dispersing agents may also be used where
necessary.

[0174] The emulsion polymerization is a method in which an amphiphilic
substance such as a surfactant is added in the water phase, and then an
oil phase is added to the water phase. The high pressure emulsification
method is a method in which a water phase, an oil phase and an
amphiphilic substance such as a surfactant are preliminarily mixed, and
the resulting mixture is emulsified with a high pressure emulsifying
machine such as a homogenizer to yield an aqueous emulsion. The inversion
emulsification method is a method in which an amphiphilic substance such
as a surfactant is dissolved or dispersed in an oil phase, and a water
phase is added to the oil phase to yield an O/W type emulsion. The
continuous phase is inverted from water to oil (inverse phase) midway
through the emulsification, and hence this emulsification is referred to
as the phase inversion emulsification. In this connection, the
aforementioned surfactant is not limited to the following examples;
however, examples of such a surfactant include: sodium alkylsulfonate,
alkyl sulfate ester sodium, alkyl ether sulfate ester sodium,
polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether,
alkylamino fatty acid sodium salt and alkyl trimethyl ammonium salt.

[0175] When the light curable aqueous emulsion is prepared by using the
aforementioned cross-linked urethane(meth)acrylate, either of the
emulsion formation and the cross-linking reaction may come first. In
particular, when the cross-linking reaction follows the establishment of
the emulsified condition, gelification can be effectively prevented;
hence, it is preferable to perform the cross-linking reaction in the
emulsion condition following emulsification.

[0176] The counterpart of the cross-linking reaction based on the
cross-linking agent is not limited to the urethane(meth)acrylate
represented by the foregoing general formula (1), but may also be other
included substances such as the aforementioned compound having in the
molecule thereof three or more (meth)acryloyl groups.

[0177] As described above, the light curable aqueous emulsion according to
the present embodiment using the urethane(meth)acrylate of the
aforementioned embodiment can provide a light curable aqueous emulsion
which is low in viscosity, excellent in curability, light curable in the
presence of water, and additionally excellent in hydrolysis resistance.
In particular, in the form in which the compound having a radical
polymerizable group(s) and the photoradical polymerization initiator are
included in the micelles formed by the urethane(meth)acrylate of the
aforementioned embodiment, the concerned light curable aqueous emulsion
can acquire the excellent curability and the performance of being light
curable even in the presence of a predetermined concentration of water,
wherein such performance is not found in conventional light curable
aqueous emulsions. The urethane(meth)acrylate forming the micelles of the
light curable aqueous emulsion of the present embodiment is capable of
densely orienting due to the structure thereof, and further strong
bonding force due to hydrogen bond probably operates between the arranged
urethane(meth)acrylate molecules because the urethane(meth)acrylate has
the urethane bonds (urethane groups) in the hydrophobic moiety in the
structure thereof. Probably because of this, there has been obtained a
stable emulsion in which the included substances in the micelles hardly
leak and hydrolysis hardly occurs.

[0178] The reasons for the fact that the light curable aqueous emulsion of
the present embodiment is excellent in photopolymerizability (curability)
and additionally is polymerized (cured) with light even in the presence
of a predetermined concentration of water are not yet clear; however, the
reasons are inferred as follows. As described above, the light curable
aqueous emulsion of the present embodiment takes the condition such that
the urethane(meth)acrylate of the aforementioned embodiment forms in
water spherical micelles including in the core thereof the compound
having a radical polymerizable group(s) and the photoradical
polymerization initiator; in this condition, light irradiation does not
cause polymerization (curing). When the light curable aqueous emulsion is
applied to a substrate and dried so as to have a predetermined
concentration, light irradiation can cause polymerization (curing) even
in the condition such that water remains, and thus a satisfactory
adhesion to the substrate can be obtained. This is presumably because the
decrease of the water concentration allows the spherical micelles to form
a lamellar structure under the condition that the spherical micelles hold
in the interior thereof the compound having a radical polymerizable
group(s) and the photoradical polymerization initiator; and irradiation
of the lamellar structure with light allows the photoradical
polymerization initiator in the interior of the lamellar structure to be
the initiator radical, and the initiator radical attacks the compound
having a radical polymerizable group(s) and the acryloyl group of the
urethane(meth)acrylate of the aforementioned embodiment to cause a chain
reaction. This presumption is made for the purpose of describing the
curability of the light curable aqueous emulsion of the present
embodiment, but is not construed to limit the light curable aqueous
emulsion of the present embodiment.

[0179] Production Method of Coating Film

[0180] An embodiment of the present invention relates to a production
method of a coating film. The concerned production method includes an
application step and a curing step. First, in the application step, the
light curable aqueous emulsion of the aforementioned embodiment is used
as a coating liquid, and the coating liquid is applied onto a substrate
with a coating tool or a coating machine such as a bar coater. In this
application, the application thickness is appropriately determined
according to the intended use of the coating film.

[0181] Next, the curing step is a step in which the applied film formed in
the coating step is cured by irradiating the applied film with light
having a specific wavelength to form a coating film. By irradiating the
applied film on a printing medium with light falling in a specific
wavelength range, a light curing reaction (photoradical polymerization)
is caused to produce a cured coating film. The light falling in a
specific wavelength range is preferably ultraviolet (UV) light. The
specific wavelength range (ultraviolet range) is preferably a range from
360 to 410 nm and more preferably a range from 380 to 400 nm. The
wavelength range falling within the aforementioned range enables to
obtain more excellent curability.

[0182] For example, mercury lamps and metal halide lamps are widely known
as the light-emitting light sources falling in the aforementioned
wavelength range. On the other hand, from the viewpoint of environmental
protection, mercury-free light sources are strongly demanded; replacement
of mercury lamps with ultraviolet light emitting devices of GaN-based
semiconductor is proceeded. Light-emitting diodes (LEDs) and laser diodes
(LDs) are small in size, high in efficiency and long in operating life,
and hence are being used. Because of the aforementioned reasons,
light-emitting diodes (LEDs) each having a peak wavelength in a range
from 360 to 400 nm are preferable.

[0183] The aforementioned substrate is not particularly limited; however,
examples of the substrate include: plastic substrates (plates, films and
molded articles) made of polymers such as polyvinyl chloride (PVC),
polyethylene, polypropylene and polyethylene terephthalate (PET); metal
plates made of metals such as iron, silver, copper and aluminum; metal
plates and plastic films prepared by vapor deposition of these various
metals; plates made of alloys such as stainless steel and brass; and
ceramics. High-quality paper and paper used in running on, and various
paper media are also preferably usable.

[0184] The aforementioned coating liquid may include an additive such as a
leveling agent according to the substrate. For example, as a
silicone-based leveling agent, a polyester-modified silicone or a
polyether-modified silicone can be used; in particular, it is preferable
to use polyether-modified polydimethylsiloxane or polyester-modified
polydimethylsiloxane. By using these, it is possible to prevent the
repelling of the coating liquid on a substrate having liquid repellency
such as a PVC substrate. Specific examples of the aforementioned
silicone-based leveling agent may include: BYK-347, BYK-348, BYK-UV3500,
3510, 3530 and 3570 (manufactured by Byk-Chemie Japan Co., Ltd.).

[0185] The coating liquid in the present embodiment can be used for
paints, coating agents, adhesives and the like.

EXAMPLES

[0186] Hereinafter, the embodiments of the present invention are more
specifically described with reference to Examples, but the embodiments of
present invention are not limited only to these Examples.

[0219] The urethane acrylates used in following Examples and Comparative
Examples are the urethane acrylates having respectively the structures
represented by the foregoing general formula (1) and the following
general formulas (3), (4) and (5):

##STR00001##

wherein A1 represents a structure derived from a hydroxyl
group-containing acrylate having one or more acryloyl groups, B1
represents a structure derived from diisocyanate, C2 represents a
structure derived from diol, and D2 and D3 each represent a
structure derived from a polyoxyethylene glycol with one terminal thereof
blocked with a methyl group (hereinafter, also referred to as
polyoxyethylene glycol monomethyl ether), of the compounds represented by
the foregoing general formula (2).

Synthesis of Amphiphilic Urethane Acrylates

Example 1

Synthesis of Amphiphilic Urethane Acrylate (a)

[0220] In a reaction vessel equipped with a stirrer, a condenser tube, a
dropping funnel and an air introduction tube, 444.6 parts by mass of IPDI
and 202.3 parts by mass of 1,12-dodecanediol were placed, and while the
resulting mixture was being stirred, 0.26 part by mass of tin octylate
was added to the mixture, the temperature inside the reaction vessel was
increased to 90° C., and the resulting mixture was allowed to
react for 1.5 hours. Then, 200.0 parts by mass of methoxy PEG 400, 200.0
parts by mass of methoxy PEG 1000 and 0.42 part by mass of tin octylate
were added to the reaction mixture, and the resulting mixture was allowed
to react further for 1.5 hours. Next, in the reaction vessel, 634.3 parts
by mass of PPG acrylate, 0.84 part by mass of methoquinone (hydroquinone
monomethyl ether) and 0.67 part by mass of tin octylate were placed and
mixed, and under air bubbling, the temperature inside the reaction vessel
was increased to 85° C. and the resulting mixture was allowed to
react for 3 hours. Then, the reaction mixture was cooled to yield the
amphiphilic urethane acrylate (a) represented by the foregoing general
formula (1). The weight average molecular weight of the urethane acrylate
(a) was found to be 3,200.

Example 2

Synthesis of Amphiphilic Urethane Acrylate (b)

[0221] In the same reaction vessel as in Example 1, 444.6 parts by mass of
IPDI and 202.3 parts by mass of 1,12-dodecanediol were placed, and while
the resulting mixture was being stirred, 0.26 part by mass of tin
octylate was added to the mixture, the temperature inside the reaction
vessel was increased to 90° C., and the resulting mixture was
allowed to react for 1.5 hours. Then, 200.0 parts by mass of methoxy PEG
400, 200.0 parts by mass of methoxy PEG 1000 and 0.42 part by mass of tin
octylate were added to the reaction mixture, and the resulting mixture
was allowed to react further for 1.5 hours. Next, in the reaction vessel,
594.4 parts by mass of pentaerythritol triacrylate, 0.82 part by mass of
methoquinone and 0.66 part by mass of tin octylate were placed and mixed,
and under air bubbling, the temperature inside the reaction vessel was
increased to 85° C. and the resulting mixture was allowed to react
for 3 hours. Then, the reaction mixture was cooled to yield the
amphiphilic urethane acrylate (b) represented by the foregoing general
formula (1). The weight average molecular weight of the urethane acrylate
(b) was found to be 3,800.

Example 3

Synthesis of Amphiphilic Urethane Acrylate (c)

[0222] In the same reaction vessel as in Example 1, 444.6 parts by mass of
IPDI and 202.3 parts by mass of 1,12-dodecanediol were placed, and while
the resulting mixture was being stirred, 0.26 part by mass of tin
octylate was added to the mixture, the temperature inside the reaction
vessel was increased to 90° C., and the resulting mixture was
allowed to react for 1.5 hours. Then, 200.0 parts by mass of methoxy PEG
400, 200.0 parts by mass of methoxy PEG 1000 and 0.42 part by mass of tin
octylate were added to the reaction mixture, and the resulting mixture
was allowed to react further for 1.5 hours. Next, in the reaction vessel,
1300.0 parts by mass of dipentaerythritol pentaacrylate, 1.17 parts by
mass of methoquinone and 0.94 part by mass of tin octylate were placed
and mixed, and under air bubbling, the temperature inside the reaction
vessel was increased to 85° C. and the resulting mixture was
allowed to react for 3 hours. Then, the reaction mixture was cooled to
yield the amphiphilic urethane acrylate (c) represented by the foregoing
general formula (1). The weight average molecular weight of the urethane
acrylate (c) was found to be 5,300.

Example 4

Synthesis of Amphiphilic Urethane Acrylate (d)

[0223] In the same reaction vessel as in Example 1, 444.6 parts by mass of
IPDI and 202.3 parts by mass of 1,12-dodecanediol were placed, and while
the resulting mixture was being stirred, 0.26 part by mass of tin
octylate was added to the mixture, the temperature inside the reaction
vessel was increased to 90° C., and the resulting mixture was
allowed to react for 1.5 hours. Then, 700.0 parts by mass of methoxy PEG
1000 and 0.54 part by mass of tin octylate were added to the reaction
mixture, and the resulting mixture was allowed to react further for 1.5
hours. Next, in the reaction vessel, 1300.0 parts by mass of
dipentaerythritol pentaacrylate, 1.32 parts by mass of methoquinone and
1.06 parts by mass of tin octylate were placed and mixed, and under air
bubbling, the temperature inside the reaction vessel was increased to
85° C. and the resulting mixture was allowed to react for 3 hours.
Then, the reaction mixture was cooled to yield the amphiphilic urethane
acrylate (d) represented by the foregoing general formula (1). The weight
average molecular weight of the urethane acrylate (d) was found to be
5,600.

Example X

Synthesis of Amphiphilic Urethane Acrylate (e)

[0224] In the same reaction vessel as in Example 1, 444.6 parts by mass (2
moles) of IPDI and 400.0 parts by mass of polypropylene glycol having a
weight average molecular weight of 400 were placed, and while the
resulting mixture was being stirred, 0.34 part by mass of tin octylate
was added to the mixture, the temperature inside the reaction vessel was
increased to 90° C., and the resulting mixture was allowed to
react for 1.5 hours. Then, 1400.0 parts by mass of methoxy PEG 2000 and
0.90 part by mass of tin octylate were added to the reaction mixture, and
the resulting mixture was allowed to react further for 1.5 hours. Next,
in the reaction vessel, 1300.0 parts by mass of dipentaerythritol
pentaacrylate, 1.77 parts by mass of methoquinone and 2.13 parts by mass
of tin octylate were placed and mixed, and under air bubbling, the
temperature inside the reaction vessel was increased to 85° C. and
the resulting mixture was allowed to react for 3 hours. Then, the
reaction mixture was cooled to yield the amphiphilic urethane acrylate
(e) represented by the foregoing general formula (1). The weight average
molecular weight of the urethane acrylate (e) was found to be 9,000.

Comparative Example 1

Synthesis of Urethane Acrylate (p)

[0225] In the same reaction vessel as in Example 1, 444.6 parts by mass of
IPDI and 1000.0 parts by mass of polyethylene glycol (PEG 1000,
manufactured by NOF Corp.) were placed, and while the resulting mixture
was being stirred, 0.58 part by mass of tin octylate was added to the
mixture, the temperature inside the reaction vessel was increased to
90° C., and the resulting mixture was allowed to react for 1.5
hours. Then, 2400.0 parts by mass of dipentaerythritol pentaacrylate,
1.92 parts by mass of methoquinone and 1.54 parts by mass of tin octylate
were placed in the reaction vessel and mixed, and under air bubbling, the
temperature inside the reaction vessel was increased to 85° C. and
the resulting mixture was allowed to react for 3 hours. Then, the
reaction mixture was cooled to yield the urethane acrylate (p). The
urethane acrylate (p) is a urethane acrylate in which both terminal
groups are each an acryloyl group, and is represented by the foregoing
general formula (3). The weight average molecular weight of the urethane
acrylate (p) was found to be 10,500.

Comparative Example 2

Synthesis of Urethane Acrylate (q)

[0226] In the same reaction vessel as in Example 1, 578.0 parts by mass of
the trimer of HMDI (coronate HXR, manufactured by Nippon Polyurethane
Industry Co., Ltd.), 200.0 parts by mass of methoxy PEG 400 and 200.0
parts by mass of methoxy PEG 1000 were placed, and while the resulting
mixture was being stirred, 0.39 part by mass of tin octylate was added to
the mixture, the temperature inside the reaction vessel was increased to
75° C., and the resulting mixture was allowed to react for 1.5
hours. Then, 1051.6 parts by mass of pentaerythritol triacrylate, 1.01
parts by mass of methoquinone and 0.81 part by mass of tin octylate were
placed in the reaction vessel and mixed, and under air bubbling, the
temperature inside the reaction vessel was increased to 80° C. and
the resulting mixture was allowed to react for 2 hours. Then, the
reaction mixture was cooled to yield the amphiphilic urethane acrylate
(q). The urethane acrylate (q) is a urethane acrylate in which one
terminal group is an acryloyl group and for which a trifunctional
isocyanate was used, and is represented by the foregoing general formula
(4). The weight average molecular weight of the urethane acrylate (q) was
found to be 7,400.

Comparative Example 3

Synthesis of Urethane Acrylate (s)

[0227] In the same reaction vessel as in Example 1, 444.6 parts by mass of
IPDI and 62.1 parts by mass of ethylene glycol were placed, and while the
resulting mixture was being stirred, 0.20 part by mass of tin octylate
was added to the mixture, the temperature inside the reaction vessel was
increased to 90° C., and the resulting mixture was allowed to
react for 1.5 hours. Then, 700.0 parts by mass of methoxy PEG 1000 and
0.48 part by mass of tin octylate were added to the reaction mixture, and
the resulting mixture was allowed to react further for 1.5 hours. Then,
634.3 parts by mass of PPG acrylate, 0.92 parts by mass of methoquinone
and 0.68 part by mass of tin octylate were placed in the reaction vessel
and mixed, and under air bubbling, the temperature inside the reaction
vessel was increased to 85° C. and the resulting mixture was
allowed to react for 3 hours. Then, the reaction mixture was cooled to
yield the urethane acrylate (s) having a structure analogous to the
structure represented by the foregoing general formula (1). Specifically,
the urethane acrylate (s) has a structure analogous to the structure
represented by the foregoing general formula (1) in the sense that the
urethane acrylate (s) is a urethane acrylate in which the number of
carbon atoms in "C1" in the foregoing general formula (1) is 2, but
the urethane acrylate (s) does not have the structure itself represented
by the general formula (1). The weight average molecular weight of the
urethane acrylate (s) was found to be 3,000.

Comparative Example 4

Synthesis of Urethane Acrylate (t)

[0228] In the same reaction vessel as in Example 1, 222.3 parts by mass of
IPDI and 700.0 parts by mass of methoxy PEG 1000 were placed, and while
the resulting mixture was being stirred, 0.48 part by mass of tin
octylate was added to the mixture, the temperature inside the reaction
vessel was increased to 90° C., and the resulting mixture was
allowed to react for 1.5 hours. Then, 634.3 parts by mass of PPG
acrylate, 0.78 part by mass of methoquinone and 0.62 part by mass of tin
octylate were added in the reaction vessel and mixed, and under air
bubbling, the temperature inside the reaction vessel was increased to
85° C. and the resulting mixture was allowed to react for 3 hours.
Then, the reaction mixture was cooled to yield the urethane acrylate (t)
represented by the foregoing general formula (5). The urethane acrylate
(t) is a urethane acrylate free from diol residues. The weight average
molecular weight of the urethane acrylate (t) was found to be 2,300.

Production Example 1

Synthesis of Urethane Acrylate for Fixing

[0229] In the same reaction vessel as in Example 1, 444.6 parts by mass (2
moles) of IPDI and 900.0 parts by mass (1 mole) of an aromatic polyester
diol (weight average molecular weight: 900, trade name: YG-108,
manufactured by Adeka Corp.) were placed, and while the resulting mixture
was being stirred, 0.27 part by mass of tin octylate was added to the
mixture, the temperature inside the reaction vessel was increased to
85° C., and the resulting mixture was allowed to react for 2
hours. Then, 232.3 parts by mass (2 moles) of 2-hydroxyethyl acrylate,
0.79 part by mass of methoquinone and 0.63 part by mass of tin octylate
were placed in the reaction vessel and mixed, and under air bubbling, the
temperature inside the reaction vessel was increased to 85° C. and
the resulting mixture was allowed to react for 2 hours. Then, the
reaction mixture was cooled to yield the urethane acrylate. The weight
average molecular weight of the urethane acrylate was found to be 5,000.

[0232] In the same reaction vessel as in Example 1, 36.7 parts by mass of
the amphiphilic urethane acrylate (b) obtained above and 3.3 parts by
mass of a photoradical polymerization initiator (TPO) were placed, and
while the resulting mixture was being mixed, the temperature inside the
vessel was increased to 80° C. and maintained at 80° C. for
2 hours. Next, the temperature inside the vessel was cooled to 50°
C., and then, while the mixture was being stirred, 60 parts by mass of
deionized water was added to the mixture, and the mixture was maintained
at 40° C. for 1 hour to yield the light curable aqueous emulsion
(b-1) containing 40% of a nonvolatile content (the amphiphilic urethane
acrylate (b) and the photoradical polymerization initiator (TPO)) (see
Table 1).

Example 6

Preparation of a Light Curable Aqueous Emulsion (c-1)

[0233] In the same reaction vessel as in Example 1, 36.7 parts by mass of
the amphiphilic urethane acrylate (c) obtained above and 3.3 parts by
mass of a photoradical polymerization initiator (TPO) were placed, and
while the resulting mixture was being mixed, the temperature inside the
vessel was increased to 80° C. and maintained at 80° C. for
2 hours. Next, the temperature inside the vessel was cooled to 50°
C., and then, while the mixture was being stirred, 60 parts by mass of
deionized water was added to the mixture, and the mixture was maintained
at 40° C. for 1 hour to yield the light curable aqueous emulsion
(c-1) containing 40% of a nonvolatile content (the amphiphilic urethane
acrylate (c) and the photoradical polymerization initiator (TPO)) (see
Table 1).

Example 7

Preparation of a Light Curable Aqueous Emulsion (a-1)

[0234] In the same reaction vessel as in Example 1, 28.5 parts by mass of
the amphiphilic urethane acrylate (a) obtained above, 9.5 parts by mass
of dipentaerythritol pentaacrylate and 2.0 parts by mass of a
photoradical polymerization initiator (TPO) were placed, and while the
resulting mixture was being mixed, the temperature inside the vessel was
increased to 80° C. and maintained at 80° C. for 2 hours.
Next, the temperature inside the vessel was cooled to 50° C., and
then, while the mixture was being stirred, 60 parts by mass of deionized
water was added to the mixture, and the mixture was maintained at
40° C. for 1 hour to yield the light curable aqueous emulsion
(a-1) containing 40% of a nonvolatile content (the amphiphilic urethane
acrylate (a), dipentaerythritol pentaacrylate and the photoradical
polymerization initiator (TPO)) (see Table 2).

Example 8

Preparation of a Light Curable Aqueous Emulsion (d-1)

[0235] In the same reaction vessel as in Example 1, 27.5 parts by mass of
the amphiphilic urethane acrylate (d) obtained above, 9.2 parts by mass
of dipentaerythritol hexaacrylate and 3.3 parts by mass of a photoradical
polymerization initiator (TPO) were placed, and while the resulting
mixture was being mixed, the temperature inside the vessel was increased
to 80° C. and maintained at 80° C. for 2 hours. Next, the
temperature inside the vessel was cooled to 50° C., and then,
while the mixture was being stirred, 60 parts by mass of deionized water
was added to the mixture, and the mixture was maintained at 40° C.
for 1 hour to yield the light curable aqueous emulsion (d-1) containing
40% of a nonvolatile content (the amphiphilic urethane acrylate (d),
dipentaerythritol diacrylate and the photoradical polymerization
initiator (TPO)) (see Table 2).

Example 9

Preparation of a Light Curable Aqueous Emulsion (d-2)

[0236] In the same reaction vessel as in Example 1, 27.5 parts by mass of
the amphiphilic urethane acrylate (d) obtained above, 9.2 parts by mass
of polypentaerythritol polyacrylate and 3.3 parts by mass of a
photoradical polymerization initiator (TPO) were placed, and while the
resulting mixture was being mixed, the temperature inside the vessel was
increased to 80° C. and maintained at 80° C. for 2 hours.
Next, the temperature inside the vessel was cooled to 50° C., and
then, while the mixture was being stirred, 60 parts by mass of deionized
water was added to the mixture, and the mixture was maintained at
40° C. for 1 hour to yield the light curable aqueous emulsion
(d-2) containing 40% of a nonvolatile content (the amphiphilic urethane
acrylate (d), polypentaerythritol polyacrylate and the photoradical
polymerization initiator (TPO)) (see Table 2).

Example 10

Preparation of a Light Curable Aqueous Emulsion (d-3)

[0237] In the same reaction vessel as in Example 1, 27.5 parts by mass of
the amphiphilic urethane acrylate (d) obtained above, 9.2 parts by mass
of dendrimer acrylate and 3.3 parts by mass of a photoradical
polymerization initiator (TPO) were placed, and while the resulting
mixture was being mixed, the temperature inside the vessel was increased
to 80° C. and maintained at 80° C. for 2 hours. Next, the
temperature inside the vessel was cooled to 50° C., and then,
while the mixture was being stirred, 60 parts by mass of deionized water
was added to the mixture, and the mixture was maintained at 40° C.
for 1 hour to yield the light curable aqueous emulsion (d-3) containing
40% of a nonvolatile content (the amphiphilic urethane acrylate (d),
dendrimer acrylate and the photoradical polymerization initiator (TPO))
(see Table 2).

Example 11

Preparation of a Light Curable Aqueous Emulsion (d-4)

[0238] In the same reaction vessel as in Example 1, 27.5 parts by mass of
the amphiphilic urethane acrylate (d) obtained above, 9.2 parts by mass
of decafunctional urethane acrylate and 3.3 parts by mass of a
photoradical polymerization initiator (TPO) were placed, and while the
resulting mixture was being mixed, the temperature inside the vessel was
increased to 80° C. and maintained at 80° C. for 2 hours.
Next, the temperature inside the vessel was cooled to 50° C., and
then, while the mixture was being stirred, 60 parts by mass of deionized
water was added to the mixture, and the mixture was maintained at
40° C. for 1 hour to yield the light curable aqueous emulsion
(d-4) containing 40% of a nonvolatile content (the amphiphilic urethane
acrylate (d), decafunctional urethane polyacrylate and the photoradical
polymerization initiator (TPO)) (see Table 2).

Example 12

Preparation of a Light Curable Aqueous Emulsion (d-2-1)

[0239] The light curable aqueous emulsion (d-2-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (d-2) containing 40% of a nonvolatile content obtained in
aforementioned Example 9 (see Table 6).

Example 13

Preparation of a Light Curable Aqueous Emulsion (d-5-1)

[0240] In the same reaction vessel as in Example 1, 27.4 parts by mass of
the amphiphilic urethane acrylate (d) obtained above, 9.1 parts by mass
of polypentaerythritol polyacrylate, 3.3 parts by mass of a photoradical
polymerization initiator (TPO) and 0.13 part by mass of a fluorescent
brightening agent (KCB) were placed, and while the resulting mixture was
being mixed, the temperature inside the vessel was increased to
80° C. and maintained at 80° C. for 2 hours. Next, the
temperature inside the vessel was cooled to 50° C., and then,
while the mixture was being stirred, 60 parts by mass of deionized water
was added to the mixture, and the mixture was maintained at 40° C.
for 1 hour to yield the light curable aqueous emulsion (d-5) containing
40% of a nonvolatile content (the amphiphilic urethane acrylate (d),
polypentaerythritol polyacrylate, the photoradical polymerization
initiator (TPO) and the fluorescent brightening agent (KCB)) (for the
foregoing, see Table 5). The light curable aqueous emulsion (d-5-1) for
the evaluation test was obtained by adding 0.1 part by mass of BYK 348
and 69.9 parts by mass of deionized water to 30 parts by mass of the
light curable aqueous emulsion (d-5) containing 40% of a nonvolatile
content (for the foregoing, see Table 6).

Example 14

Preparation of a Light Curable Aqueous Emulsion (d-6-1)

[0241] In the same reaction vessel as in Example 1, 26.2 parts by mass of
the amphiphilic urethane acrylate (d) obtained above, 8.7 parts by mass
of polypentaerythritol polyacrylate and 3.3 parts by mass of a
photoradical polymerization initiator (TPO) were placed, and while the
resulting mixture was being mixed, the temperature inside the vessel was
increased to 80° C. and maintained at 80° C. for 2 hours.
Next, the temperature inside the vessel was cooled to 50° C., and
then, while the mixture was being stirred, 1.7 parts by mass of a
cross-linking agent (PEMP) was added to the mixture, and the mixture was
continuously stirred as it was for 15 minutes. Then, 60 parts by mass of
deionized water was added to the mixture, the mixture was maintained at
50° C. for 1 hour, then the temperature inside the vessel was
increased to 80° C., and the mixture was maintained at 80°
C. for 6 hours to yield the light curable aqueous emulsion (d-6)
containing 40% of a nonvolatile content (the amphiphilic urethane
acrylate (d), polypentaerythritol polyacrylate, the photoradical
polymerization initiator (TPO) and the cross-linking agent (PEMP)). The
emulsion was subjected to a GPC measurement to identify a cross-linked
urethane acrylate having a weight average molecular weight of 8,500 (for
the foregoing, see Table 5).

[0242] The light curable aqueous emulsion (d-6-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (d-6) containing 40% of a nonvolatile content (for the
foregoing, see Table 6).

Example 15

Preparation of a Light Curable Aqueous Emulsion (d-7-1)

[0243] In the same reaction vessel as in Example 1, 26.1 parts by mass of
the amphiphilic urethane acrylate (d) obtained above, 8.7 parts by mass
of polypentaerythritol polyacrylate, 3.3 parts by mass of a photoradical
polymerization initiator (TPO) and 0.07 part by mass of a fluorescent
brightening agent (KCB) were placed, and while the resulting mixture was
being mixed, the temperature inside the vessel was increased to
80° C. and maintained at 80° C. for 2 hours. Next, the
temperature inside the vessel was cooled to 50° C., and then,
while the mixture was being stirred, 1.7 parts by mass of a cross-linking
agent (PEMP) was added to the mixture, and the mixture was continuously
stirred as it was for 15 minutes. Then, 60 parts by mass of deionized
water was added to the mixture, the mixture was maintained at 50°
C. for 1 hour, then the temperature inside the vessel was increased to
80° C., and the mixture was maintained at 80° C. for 6
hours to yield the light curable aqueous emulsion (d-7) containing 40% of
a nonvolatile content (the amphiphilic urethane acrylate (d),
polypentaerythritol polyacrylate, the photoradical polymerization
initiator (TPO), the fluorescent brightening agent (KCB) and the
cross-linking agent (PEMP)). The emulsion was subjected to a GPC
measurement to identify a cross-linked urethane acrylate having a weight
average molecular weight of 16,000 (for the foregoing, see Table 5).

[0244] The light curable aqueous emulsion (d-7-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (d-7) containing 40% of a nonvolatile content (for the
foregoing, see Table 6).

Example 16

Preparation of a Light Curable Aqueous Emulsion (e-1-1)

[0245] In the same reaction vessel as in Example 1, 23.3 parts by mass of
the amphiphilic urethane acrylate (e) obtained above, 8.3 parts by mass
of polypentaerythritol polyacrylate, 1.7 parts by mass of the urethane
acrylate for fixing, 5.0 parts by mass of a photoradical polymerization
initiator (TPO), 1.7 parts by mass of a photoradical polymerization
initiator (DETX) and 0.07 part by mass of a fluorescent brightening agent
(KCB) were placed, and while the resulting mixture was being mixed, the
temperature inside the vessel was increased to 80° C. and
maintained at 80° C. for 2 hours. Next, the temperature inside the
vessel was cooled to 50° C., and then, while the mixture was being
stirred, 60 parts by mass of deionized water was added to the mixture,
and the mixture was maintained at 50° C. for 1 hour to yield the
light curable aqueous emulsion (e-1) containing 40% of a nonvolatile
content (the amphiphilic urethane acrylate (e), polypentaerythritol
polyacrylate, the urethane acrylate for fixing, the photoradical
polymerization initiators (TPO, DETX) and the fluorescent brightening
agent (KCB)) (for the foregoing, see Table 5).

[0246] The light curable aqueous emulsion (e-1-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (e-1) containing 40% of a nonvolatile content (for the
foregoing, see Table 6).

Example 17

Preparation of a Light Curable Aqueous Emulsion (e-2-1)

[0247] In the same reaction vessel as in Example 1, 23.9 parts by mass of
the amphiphilic urethane acrylate (e) obtained above, 10.3 parts by mass
of polypentaerythritol polyacrylate, 3.3 parts by mass of a photoradical
polymerization initiator (TPO) and 0.07 part by mass of a fluorescent
brightening agent (KCB) were placed, and while the resulting mixture was
being mixed, the temperature inside the vessel was increased to
80° C. and maintained at 80° C. for 2 hours. Next, the
temperature inside the vessel was cooled to 50° C., and then,
while the mixture was being stirred, 2.4 parts by mass of a cross-linking
agent (PEMP) was added to the mixture, and the mixture was continuously
stirred as it was for 15 minutes. Then, 60 parts by mass of deionized
water was added to the mixture, the mixture was maintained at 50°
C. for 1 hour, then the temperature inside the vessel was increased to
80° C., and the mixture was maintained at 80° C. for 6
hours to yield the light curable aqueous emulsion (e-2) containing 40% of
a nonvolatile content (the amphiphilic urethane acrylate (e),
polypentaerythritol polyacrylate, the photoradical polymerization
initiator (TPO), the fluorescent brightening agent (KCB) and the
cross-linking agent (PEMP)). The emulsion was subjected to a GPC
measurement to identify a cross-linked urethane acrylate having a weight
average molecular weight of 20,000 (for the foregoing, see Table 5).

[0248] The light curable aqueous emulsion (e-2-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (e-2) containing 40% of a nonvolatile content (for the
foregoing, see Table 6).

Example 18

Preparation of a Light Curable Aqueous Emulsion (e-3-1)

[0249] In the same reaction vessel as in Example 1, 21.6 parts by mass of
the amphiphilic urethane acrylate (e) obtained above, 9.2 parts by mass
of polypentaerythritol polyacrylate, 6.7 parts by mass of a photoradical
polymerization initiator (TPO) and 0.06 part by mass of a fluorescent
brightening agent (KCB) were placed, and while the resulting mixture was
being mixed, the temperature inside the vessel was increased to
80° C. and maintained at 80° C. for 2 hours. Next, the
temperature inside the vessel was cooled to 50° C., and then,
while the mixture was being stirred, 2.5 parts by mass of a cross-linking
agent (PEMP) was added to the mixture, and the mixture was continuously
stirred as it was for 15 minutes. Then, 60 parts by mass of deionized
water was added to the mixture, the mixture was maintained at 50°
C. for 1 hour, then the temperature inside the vessel was increased to
80° C., and the mixture was maintained at 80° C. for 6
hours to yield the light curable aqueous emulsion (e-3) containing 40% of
a nonvolatile content (the amphiphilic urethane acrylate (e),
polypentaerythritol polyacrylate, the photoradical polymerization
initiator (TPO), the fluorescent brightening agent (KCB) and the
cross-linking agent (PEMP)). The emulsion was subjected to a GPC
measurement to identify a cross-linked urethane acrylate having a weight
average molecular weight of 22,000 (for the foregoing, see Table 5).

[0250] The light curable aqueous emulsion (e-3-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (e-3) containing 40% of a nonvolatile content (for the
foregoing, see Table 6).

Example 19

Preparation of a Light Curable Aqueous Emulsion (e-4-1)

[0251] In the same reaction vessel as in Example 1, 21.6 parts by mass of
the amphiphilic urethane acrylate (e) obtained above, 9.2 parts by mass
of polypentaerythritol polyacrylate, 5.0 parts by mass of a photoradical
polymerization initiator (TPO), 1.7 parts by mass of a photoradical
polymerization initiator (DETX) and 0.06 part by mass of a fluorescent
brightening agent (KCB) were placed, and while the resulting mixture was
being mixed, the temperature inside the vessel was increased to
80° C. and maintained at 80° C. for 2 hours. Next, the
temperature inside the vessel was cooled to 50° C., and then,
while the mixture was being stirred, 2.5 parts by mass of a cross-linking
agent (PEMP) was added to the mixture, and the mixture was continuously
stirred as it was for 15 minutes. Then, 60 parts by mass of deionized
water was added to the mixture, the mixture was maintained at 50°
C. for 1 hour, then the temperature inside the vessel was increased to
80° C., and the mixture was maintained at 80° C. for 6
hours to yield the light curable aqueous emulsion (e-4) containing 40% of
a nonvolatile content (the amphiphilic urethane acrylate (e),
polypentaerythritol polyacrylate, the photoradical polymerization
initiators (TPO, DETX), the fluorescent brightening agent (KCB) and the
cross-linking agent (PEMP)). The emulsion was subjected to a GPC
measurement to identify a cross-linked urethane acrylate having a weight
average molecular weight of 22,000 (for the foregoing, see Table 5).

[0252] The light curable aqueous emulsion (e-4-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (e-4) containing 40% of a nonvolatile content (for the
foregoing, see Table 6).

Example 20

Preparation of a Light Curable Aqueous Emulsion (e-5-1)

[0253] In the same reaction vessel as in Example 1, 21.6 parts by mass of
the amphiphilic urethane acrylate (e) obtained above, 7.7 parts by mass
of polypentaerythritol polyacrylate, 1.5 parts by mass of the urethane
acrylate for fixing, 5.0 parts by mass of a photoradical polymerization
initiator (TPO) and 1.7 parts by mass of a photoradical polymerization
initiator (DETX) were placed, and while the resulting mixture was being
mixed, the temperature inside the vessel was increased to 80° C.
and maintained at 80° C. for 2 hours. Next, the temperature inside
the vessel was cooled to 50° C., and then, while the mixture was
being stirred, 2.5 parts by mass of a cross-linking agent (PEMP) was
added to the mixture, and the mixture was continuously stirred as it was
for 15 minutes. Then, 60 parts by mass of deionized water was added to
the mixture, the mixture was maintained at 50° C. for 1 hour, then
the temperature inside the vessel was increased to 80° C., and the
mixture was maintained at 80° C. for 6 hours to yield the light
curable aqueous emulsion (e-5) containing 40% of a nonvolatile content
(the amphiphilic urethane acrylate (e), polypentaerythritol polyacrylate,
the urethane acrylate for fixing, the photoradical polymerization
initiators (TPO, DETX) and the cross-linking agent (PEMP)). The emulsion
was subjected to a GPC measurement to identify a cross-linked urethane
acrylate having a weight average molecular weight of 18,000 (for the
foregoing, see Table 5).

[0254] The light curable aqueous emulsion (e-5-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (e-5) containing 40% of a nonvolatile content (for the
foregoing, see Table 6).

Example 21

Preparation of a Light Curable Aqueous Emulsion (e-6-1)

[0255] In the same reaction vessel as in Example 1, 21.6 parts by mass of
the amphiphilic urethane acrylate (e) obtained above, 7.7 parts by mass
of polypentaerythritol polyacrylate, 1.5 parts by mass of the urethane
acrylate for fixing, 5.0 parts by mass of a photoradical polymerization
initiator (TPO), 1.7 parts by mass of a photoradical polymerization
initiator (DETX) and 0.06 part by mass of a fluorescent brightening agent
(KCB) were placed, and while the resulting mixture was being mixed, the
temperature inside the vessel was increased to 80° C. and
maintained at 80° C. for 2 hours. Next, the temperature inside the
vessel was cooled to 50° C., and then, while the mixture was being
stirred, 2.5 parts by mass of a cross-linking agent (PEMP) was added to
the mixture, and the mixture was continuously stirred as it was for 15
minutes. Then, 60 parts by mass of deionized water was added to the
mixture, the mixture was maintained at 50° C. for 1 hour, then the
temperature inside the vessel was increased to 80° C., and the
mixture was maintained at 80° C. for 6 hours to yield the light
curable aqueous emulsion (e-6) containing 40% of a nonvolatile content
(the amphiphilic urethane acrylate (e), polypentaerythritol polyacrylate,
the urethane acrylate for fixing, the photoradical polymerization
initiators (TPO, DETX), the fluorescent brightening agent (KCB) and the
cross-linking agent (PEMP)). The emulsion was subjected to a GPC
measurement to identify a cross-linked urethane acrylate having a weight
average molecular weight of 18,000 (for the foregoing, see Table 5).

[0256] The light curable aqueous emulsion (e-6-1) for the evaluation test
was obtained by adding 0.1 part by mass of BYK 348 and 69.9 parts by mass
of deionized water to 30 parts by mass of the light curable aqueous
emulsion (e-6) containing 40% of a nonvolatile content (for the
foregoing, see Table 6).

Comparative Example 5

Preparation of a Light Curable Aqueous Emulsion (p-1)

[0257] In the same reaction vessel as in Example 1, 38.0 parts by mass of
the urethane acrylate (p) obtained above and 2.0 parts by mass of a
photoradical polymerization initiator (TPO) were placed, and while the
resulting mixture was being mixed, the temperature inside the vessel was
increased to 80° C. and maintained at 80° C. for 2 hours.
Next, the temperature inside the vessel was cooled to 50° C., and
then, while the mixture was being stirred, 60 parts by mass of deionized
water was added to the mixture, and the mixture was maintained at
40° C. for 1 hour to yield the light curable aqueous emulsion
(p-1) containing 40% of a nonvolatile content (the urethane acrylate (p)
and the photoradical polymerization initiator (TPO)) (see Table 3).

Comparative Example 6

Preparation of a Light Curable Aqueous Emulsion (q-1)

[0258] In the same reaction vessel as in Example 1, 38.0 parts by mass of
the urethane acrylate (q) obtained above and 2.0 parts by mass of a
photoradical polymerization initiator (TPO) were placed, and while the
resulting mixture was being mixed, the temperature inside the vessel was
increased to 80° C. and maintained at 80° C. for 2 hours.
Next, the temperature inside the vessel was cooled to 50° C., and
then, while the mixture was being stirred, 60 parts by mass of deionized
water was added to the mixture, and the mixture was maintained at
40° C. for 1 hour to yield the light curable aqueous emulsion
(q-1) containing 40% of a nonvolatile content (the urethane acrylate (q)
and the photoradical polymerization initiator (TPO)) (see Table 3).

Comparative Example 7

Preparation of a Light Curable Aqueous Emulsion (q-2)

[0259] In the same reaction vessel as in Example 1, 27.5 parts by mass of
the urethane acrylate (q) obtained above, 9.2 parts by mass of
polypentaerythritol polyacrylate and 3.3 parts by mass of a photoradical
polymerization initiator (TPO) were placed, and while the resulting
mixture was being mixed, the temperature inside the vessel was increased
to 80° C. and maintained at 80° C. for 2 hours. Next, the
temperature inside the vessel was cooled to 50° C., and then,
while the mixture was being stirred, 60 parts by mass of deionized water
was added to the mixture, and the mixture was maintained at 40° C.
for 1 hour to yield the light curable aqueous emulsion (q-2) containing
40% of a nonvolatile content (the urethane acrylate (q),
polypentaerythritol polyacrylate and the photoradical polymerization
initiator (TPO)) (see Table 3).

Comparative Example 8

Preparation of a Light Curable Aqueous Emulsion (s-1)

[0260] In the same reaction vessel as in Example 1, 38.0 parts by mass of
the urethane acrylate (s) obtained above and 2.0 parts by mass of a
photoradical polymerization initiator (TPO) were placed, and while the
resulting mixture was being mixed, the temperature inside the vessel was
increased to 80° C. and maintained at 80° C. for 2 hours.
Next, the temperature inside the vessel was cooled to 50° C., and
then, while the mixture was being stirred, 60 parts by mass of deionized
water was added to the mixture, and the mixture was maintained at
40° C. for 1 hour to yield the light curable aqueous emulsion
(s-1) containing 40% of a nonvolatile content (the urethane acrylate (s)
and the photoradical polymerization initiator (TPO)) (see Table 3).

Comparative Example 9

Preparation of a Light Curable Aqueous Emulsion (t-1)

[0261] In the same reaction vessel as in Example 1, 38.0 parts by mass of
the urethane acrylate (t) obtained above and 2.0 parts by mass of a
photoradical polymerization initiator (TPO) were placed, and while the
resulting mixture was being mixed, the temperature inside the vessel was
increased to 80° C. and maintained at 80° C. for 2 hours.
Next, the temperature inside the vessel was cooled to 50° C., and
then, while the mixture was being stirred, 60 parts by mass of deionized
water was added to the mixture, and the mixture was maintained at
40° C. for 1 hour to yield the light curable aqueous emulsion
(t-1) containing 40% of a nonvolatile content (the urethane acrylate (t)
and the photoradical polymerization initiator (TPO)) (see Table 3).

[0262] Evaluation Items

[0263] Emulsifiability

[0264] Each of the light curable aqueous emulsions prepared in the
aforementioned "Preparation of Light Curable Aqueous Emulsions" was
allowed to stand still at 40° C., and the condition variation of
the emulsion was observed. The observation results were classified
according to the following evaluation standards. The evaluation results
are shown in Tables 2, 3 and 6.

[0265] A: Even when the emulsion was allowed to stand for one week or
more, no occurrence of phase separation and precipitation was found
without any variation from the initial condition.

[0266] B: When the emulsion was allowed to stand for one week, the
occurrence of phase separation or precipitation was found.

[0267] C: Immediately after the preparation of the emulsion, the
occurrence of phase separation or precipitation was found.

[0268] The concerned evaluation targeting at the light curable aqueous
emulsion is equivalent to the evaluation of the emulsifiability of the
urethane acrylate used in the light curable aqueous emulsion.

[0269] Viscosity

[0270] Each of the light curable aqueous emulsions prepared in the
aforementioned "Preparation of Light Curable Aqueous Emulsions" was
subjected to viscosity measurement with an E-type viscometer (trade name:
TVE-20H, manufactured by Tokisangyo Co., Ltd.) under the condition that
the temperature of the light curable aqueous emulsion was set at
25° C.

[0271] Curability in Each of Examples 5 to 11 and Comparative Examples 5
to 9

[0272] Each of the aforementioned light curable aqueous emulsions of
Examples 5 to 11 and Comparative Examples 5 to 9 was applied onto a
surface-treated PET film with a bar coater so as for the application
thickness to be 10 μm; after an elapsed time of 120 seconds under the
conditions of a temperature of 25° C. and a humidity of 40%, the
applied emulsion layer was irradiated with ultraviolet light by using an
LED lamp (395 nm, 1000 mW/m2) and then the cured condition was
examined. The examination of the cured condition was performed as
follows: the tip of a cotton swab was brought into contact with the
coating surface, and when the cotton swab was moved under the conditions
that the cotton swab was pressed against the coating surface with a
pressure of 200 gf/cm2 while the cotton swab was being inclined by
45 degrees from the coating surface, the case where no scratch was formed
on the coating film was defined as the case where curing was achieved.
[0273] Application conditions: Bar coater No. 6 (film thickness under
dried condition: 4 to 6 μm)

[0274] The evaluation results are shown in Tables 1 to 3.

[0275] Curability in Each of Examples 12 to 21

[0276] Each of the light curable aqueous emulsions (of these emulsions,
the emulsions of Examples 13 to 21 are of a cross-linked type) shown in
Table 5 was evaluated as follows for the purpose of making clear the
evaluation results of the curability.

[0277] First, the light curable aqueous emulsion of aforementioned Example
9 (see Table 5) was diluted with water as shown in Table 6 in such a way
that the irradiation energy amount required for curing was 30 mJ/cm2
to 1,900 mJ/cm2.

[0278] Next, this light curable aqueous emulsion of Example 9 and the
light curable aqueous emulsions, each using a cross-linked urethane
acrylate, of Examples 13 to 21 shown in Table 6 were evaluated with
respect to curability in the same manner as described above except that a
PVC film was adopted as the substrate, the coating condition involved a
bar coater No. 9, the ultraviolet light irradiation was performed after
an elapsed time of 90 seconds and the following evaluation standards were
adopted.

[0279] AA: Less than 500 mJ/cm2

[0280] A: 500 mJ/cm2 or more and less than 1000 mJ/cm2

[0281] B: 1000 mJ/cm2 or more and less than 1500 mJ/cm2

[0282] C: 1500 mJ/cm2 or more and less than 2000 mJ/cm2

[0283] D: 2000 mJ/cm2 or more

[0284] The evaluation results are shown in Table 6.

[0285] Hydrolyzability

[0286] In a 70 mL glass sample bottle, each of the light curable aqueous
emulsions of Examples 9 and 11 was placed in an amount of 50 mL, and the
sample bottle was stoppered tightly and was allowed to stand at
40° C. for 2 weeks. Then, these light curable aqueous emulsions
were each subjected to a molecular weight measurement with GPC (trade
name: HLC-8220, manufactured by Tosoh Corp.).

[0287] When the amphiphilic urethane acrylate constituting each of the
light curable aqueous emulsions is hydrolyzed, the generation of acrylic
acid is taken to occur; accordingly, when no generation of acrylic acid
occurred, it was determined that no hydrolysis occurred (in Tables 4 and
6, denoted as "none").

[0288] Adhesiveness in Each of Examples 12 to 21

[0289] Each of the light curable aqueous emulsions of Examples 12 to 21
was applied onto a PVC film with a bar coater so as for the application
thickness to be 10 μm; after an elapsed time of 90 seconds under the
conditions of a temperature of 25° C. and a humidity of 40%, the
applied emulsion layer was irradiated with ultraviolet light by using an
LED lamp (an irradiator manufactured by Phoseon Technology, Inc., peak
wavelength: 395 nm, illuminance: 1000 mW/m2 (Gap: 6 mm), 2000
mJ/cm2). [0290] Application conditions: Bar coater No. 9 (film
thickness under dried condition: 4 to 6 μm)

[0291] A tape was bonded to each of the obtained coating films, and the
adhesiveness of each of the coating films was evaluated on the basis of
whether or not the coating film was peeled off when the tape was peeled
off. The evaluation standards are as follows.

[0295] Tables 1 to 3 show that the light curable aqueous emulsions
(Examples) each having a weight average molecular weight of 1,000 to
10,000 and using the urethane acrylate having the specific structure
represented by the foregoing general formula (1) are excellent in the
emulsifiability in water of the urethane acrylate and are each low in the
viscosity of the emulsion and excellent in the curability of the
emulsion, as compared to the light curable aqueous emulsions (Comparative
Examples) each using a conventional urethane acrylate.

[0296] As can be seen from Table 4, for each of Examples 9 and 11, no
detection peak of acrylic acid was found, and the measurement results
which were the same as the initial conditions were obtained. Accordingly,
it may be determined no hydrolysis occurred.

[0297] As can be seen from these results, the amphiphilic urethane
acrylates constituting the light curable aqueous emulsions of the present
invention are excellent in hydrolysis resistance.

[0298] Also, as can be seen from Table 6, the emulsions using specified
cross-linked urethane acrylates are extremely excellent in curability as
compared to the emulsions using non-cross-linked urethane acrylates.

[0299] From Table 6, the emulsion of Example 12 corresponding to the
emulsion obtained by diluting the emulsion of Example 9 appears to be
poor in curability. However, as shown in Example 9, the emulsion of
Example 9 was cured with an irradiation energy as small as 30
mJ/cm2, and hence is excellent in curability (see Table 2). Thus,
the present inventors have found that the emulsions of Examples 13 to 21
are extremely excellent in curability, specifically due to the
cross-linking of the specified urethane(meth)acrylates.

[0300] On the basis of the results obtained above, here is discussed the
mechanism of excellent effects achieved by the cross-linked
urethane(meth)acrylates of the present invention. For the purpose of
obtaining films excellent in curability from low molecular weight
urethane(meth)acrylates, it is required to make higher the molecular
weights by a large amount of irradiation of ultraviolet light.
Accordingly, it is inferred that the molecular weight of the
urethane(meth)acrylate made larger by cross-linking allows even a smaller
amount of ultraviolet light irradiation to result in a larger effect of
increasing the molecular weight (even the reaction of a small amount of
acryloyl groups results in insolubilization of the
urethane(meth)acrylate), and thus the curability is made more excellent.

[0301] The present invention is not limited to the aforementioned
discussion. The present inventors have verified that in the case where
used are urethane(meth)acrylates other than the amphiphilic
urethane(meth)acrylates having a specified structure in the present
invention, even when such urethane(meth)acrylates are successfully
cross-linked, no stable aqueous emulsions can be obtained.

[0302] On the basis of the results obtained above, also discussed are the
reasons for the results such that the urethane acrylates used in
Comparative Examples did not yield cross-linked urethane acrylates. In
each of Comparative Examples 5, 7 and 8, a possible reason may be such
that a cross-linking agent was not able to be included in the oil phase
because of the poor emulsifiability of the urethane acrylate, and the
urethane acrylate was gelified in the course of the reaction. In
Comparative Example 6, a possible reason may be such that the viscosity
was not low although the cross-linked urethane(meth)acrylate
(cross-linked emulsion) was able to be obtained, and the curability was
also inferred to be satisfactory. The present invention is not limited to
the aforementioned discussion.